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Indo-Western Pacific Ocean Capacitor and Coherent Climate Anomalies in Post-ENSO Summer: A Review

doi: 10.1007/s00376-015-5192-6

  • ENSO induces coherent climate anomalies over the Indo-western Pacific, but these anomalies outlast SST anomalies of the equatorial Pacific by a season, with major effects on the Asian summer monsoon. This review provides historical accounts of major milestones and synthesizes recent advances in the endeavor to understand summer variability over the Indo-Northwest Pacific region. Specifically, a large-scale anomalous anticyclone (AAC) is a recurrent pattern in post-El Niño summers, spanning the tropical Northwest Pacific and North Indian oceans. Regarding the ocean memory that anchors the summer AAC, competing hypotheses emphasize either SST cooling in the easterly trade wind regime of the Northwest Pacific or SST warming in the westerly monsoon regime of the North Indian Ocean. Our synthesis reveals a coupled ocean-atmosphere mode that builds on both mechanisms in a two-stage evolution. In spring, when the northeast trades prevail, the AAC and Northwest Pacific cooling are coupled via wind-evaporation-SST feedback. The Northwest Pacific cooling persists to trigger a summer feedback that arises from the interaction of the AAC and North Indian Ocean warming, enabled by the westerly monsoon wind regime. This Indo-western Pacific ocean capacitor (IPOC) effect explains why El Niño stages its last act over the monsoonal Indo-Northwest Pacific and casts the Indian Ocean warming and AAC in leading roles. The IPOC displays interdecadal modulations by the ENSO variance cycle, significantly correlated with ENSO at the turn of the 20th century and after the 1970s, but not in between. Outstanding issues, including future climate projections, are also discussed.
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  • Alexand er, M. A., I. Bladè, M. Newman, J. R. Lanzante, N. C. Lau, J. D. Scott, 2002: The atmospheric bridge: The influence of ENSO teleconnections on air-sea interaction over the global oceans. J. Climate, 15, 2205- 2231.10.1175/1520-0442(2002)015<2205:TABTIO>2.0.CO; El Nino-Southern Oscillation (ENSO) events, the atmospheric response to sea surface temperature (SST) anomalies in the equatorial Pacific influences ocean conditions over the remainder of the globe. This connection between ocean basins via the "atmospheric bridge" is reviewed through an examination of previous work augmented by analyses of 50 years of data from the National Centers for Environmental PredictionNational Center for Atmospheric Research (NCEP-NCAR) reanalysis project and coupled atmospheric general circulation (AGCM)-mixed layer ocean model experiments. Observational and modeling studies have now established a clear link between SST anomalies in the equatorial Pacific with those in the North Pacific, north tropical Atlantic, and Indian Oceans in boreal winter and spring. ENSO-related SST anomalies also appear to be robust in the western North Pacific during summer and in the Indian Ocean during fall. While surface heat fluxes are the key component of the atmospheric bridge driving SST anomalies, Ekman transport also creates SST anomalies in the central North Pacific although the full extent of its impact requires further study. The atmospheric bridge not only influences SSTs on interannual timescales but also affects mixed layer depth (MLD), salinity, the seasonal evolution of upper-ocean temperatures, and North Pacific SST variability at lower frequencies. The model results indicate that a significant fraction of the dominant pattern of low-frequency (>10 yr) SST variability in the North Pacific is associated with tropical forcing. AGCM experiments suggest that the oceanic feedback on the extratropical response to ENSO is complex, but of modest amplitude. Atmosphereocean coupling outside of the tropical Pacific slightly modifies the atmospheric circulation anomalies in the Pacific-North America (PNA) region but these modifications appear to depend on the seasonal cycle and airsea interactions both within and beyond the North Pacific...
    Allan R., T. Ansell, 2006: A new globally complete monthly historical gridded mean sea level pressure dataset (HadSLP2): 1850-2004. J. Climate, 19, 5816- 5842.10.1175/ An upgraded version of the Hadley Centre monthly historical mean sea level pressure (MSLP) dataset (HadSLP2) is presented. HadSLP2 covers the period from 1850 to date, and is based on numerous terrestrial and marine data compilations. Each terrestrial pressure series used in HadSLP2 underwent a series of quality control tests, and erroneous or suspect values were either corrected, where possible, or removed. Marine observations from the International Comprehensive Ocean Atmosphere Data Set were quality controlled (assessed against climatology and near neighbors) and then gridded. The final gridded form of HadSLP2 was created by blending together the processed terrestrial and gridded marine MSLP data. MSLP fields were made spatially complete using reduced-space optimal interpolation. Gridpoint error estimates were also produced. HadSLP2 was found to have generally stronger subtropical anticyclones and higher-latitude features across the Northern Hemisphere than an earlier product (HadSLP1). During the austral winter, however, it appears that the pressures in the southern Atlantic and Indian Ocean midlatitude regions are too high; this is seen in comparisons with both HadSLP1 and the 40-yr ECMWF Re-Analysis (ERA-40). Over regions of high altitude, HadSLP2 and ERA-40 showed consistent differences suggestive of potential biases in the reanalysis model, though the region over the Himalayas in HadSLP2 is biased compared with HadSLP1 and improvements are required in this region. Consistent differences were also observed in regions of sparse data, particularly over the higher latitudes of the Southern Ocean and in the southeastern Pacific. Unlike the earlier HadSLP1 product, error estimates are available with HadSLP2 to guide the user in these regions of low confidence. An evaluation of major phenomena in the climate system using HadSLP2 provided further validation of the dataset. Important climatic features/indices such as the North Atlantic Oscillation, Arctic Oscillation, North Pacific index, Southern Oscillation index, Trans-Polar index, Antarctic Oscillation, Antarctic Circumpolar Wave, East Asian Summer Monsoon index, and the Siberian High index have all been resolved in HadSLP2, with extensions back to the mid-nineteenth century.
    Alory G., S. Wijffels, and G. Meyers, 2007: Observed temperature trends in the Indian Ocean over 1960-1999 and associated mechanisms. Geophys. Res. Lett., 34,L02606, doi: 10.1029/ 2006GL028044.10.1029/[1] The linear trends in oceanic temperature from 1960 to 1999 are estimated using the new Indian Ocean Thermal Archive (IOTA), a compilation of historical temperature profiles. Widespread surface warming is found, as in other data sets, and reproduced in IPCC climate model simulations for the 20th century. This warming is particularly large in the subtropics, and extends down to 800 m around 40-50S. Models suggest the deep-reaching subtropical warming is related to a 0.5 southward shift of the subtropical gyre driven by a strengthening of the westerly winds, and associated with an upward trend in the Southern Annular Mode index. In the tropics, IOTA shows a subsurface cooling corresponding to a shoaling of the thermocline and increasing vertical stratification. Most models suggest this trend in the tropical Indian thermocline is likely associated with the observed weakening of the Pacific trade winds and transmitted to the Indian Ocean by the Indonesian throughflow.
    Annamalai H., S.-P. Xie, J. P. McCreary, and R. Murtugudde, 2005: Impact of Indian Ocean Sea surface temperature on developing El Niño. J. Climate, 18, 302- 319.
    Arai M., M. Kimoto, 2008: Simulated interannual variation in summertime atmospheric circulation associated with the East Asian monsoon. Climate Dyn., 31, 435- 447.10.1007/ reproducibility of the interannual variability of the summertime East Asian circulation is examined using an atmospheric general circulation model (AGCM). An ensemble experiment is conducted using observed sea surface temperature (SST) of recent 20 years as a lower boundary condition. The spatial pattern associated with the first principal mode of observation of geopotential height at 500 hPa is characterized by a meridional wavy pattern extending over eastern Siberia, the vicinity of Japan and the subtropical western Pacific. The principal component (PC) time series of the leading mode is represented well by a high-resolution version of the AGCM with horizontal resolution T106 and with 56 vertical levels (T106L56), while with a lower resolution version, T42 and 20 vertical levels, the reproducibility is considerably degraded. The reproducibility by the AGCM suggests the importance of SST as a boundary condition. However, the simulated interannual variations show the alternating appearance of two distinct circulation regimes, a cold summer regime and a hot summer regime, exhibiting interesting bimodality in probability density distribution in PC phase space. This implies that the system閿熺氮 response to the continuously varying boundary condition includes nonlinearity. The nature of this nonlinearity is suggested to be wave breaking in the westerly region of the high latitudes that requires high resolution for the reproduction. Using the T106L56 model, another ensemble experiment was carried out with doubled CO2. The climate change appears as an increase in residence frequency of the cold summer regime of the principal patterns of the present-day climate.
    Cai W. J., T. Cowan, 2013: Why is the amplitude of the Indian Ocean dipole overly large in CMIP3 and CMIP5 climate models? Geophys. Res. Lett.,40, 1200-1205, doi: 10.1002/grl. 50208.10.1002/[1] The Indian Ocean Dipole (IOD) affects weather and climate in many parts of the world, but a realistic simulation of the IOD in state-of-the-art climate models remains a challenge. In most models, IOD peak-season amplitudes are systematically larger than that of the observed, a bias that deterministically affects climate projections in IOD-affected regions. Understanding the cause of this bias is therefore essential for alleviating model errors and reducing uncertainty in climate projections. Here it is shown that most Coupled Model Intercomparison Project Phase Three (CMIP3) and CMIP5 models produce too strong a Bjerknes feedback in the equatorial Indian Ocean, leading to the IOD bias. The thermocline-sea surface temperature (SST) feedback exerts the strongest influence on the simulated IOD amplitude; models simulating a stronger thermocline-SST feedback systematically generate a greater IOD amplitude. The strength of the thermocline-SST feedback in most models is predominantly controlled by the climatological west-east slope of the equatorial thermocline, which features an unrealistic mean slope tilting upward toward the eastern Indian Ocean. The unrealistic thermocline structure is accompanied by too strong a mean easterly wind and an overly strong west-minus-east SST gradient. The linkage of the mean climatic conditions, feedback strength, and projected climate highlights the fundamental importance of realistically simulating these components of the climate system for reducing uncertainty in climate change projections in IOD-affected regions.
    Cao J., R. Y. Lu, J. M. Hu, and H. Wang, 2013: Spring Indian Ocean-western Pacific SST contrast and the East Asian summer rainfall anomaly. Adv. Atmos. Sci.,30, 1560-1568, doi: 10.1007/s00376-013-2298-6.10.1007/
    Chang C. P., Y. S. Zhang, and T. Li, 2000: Interannual and interdecadal variations of the East Asian summer monsoon and tropical Pacific SSTs. Part I: Roles of the subtropical ridge. J. Climate, 13, 4310- 4325.10.1175/1520-0442(2000)013<4310:IAIVOT>2.0.CO; The interannual relationship between the East Asian summer monsoon and the tropical Pacific SSTs is studied using rainfall data in the Yangtze River Valley and the NCEP reanalysis for 1951-96. The datasets are also partitioned into two periods, 1951-77 and 1978-96, to study the interdecadal variations of this relationship. A wet summer monsoon is preceded by a warm equatorial eastern Pacific in the previous winter and followed by a cold equatorial eastern Pacific in the following fall. This relationship involves primarily the rainfall during the pre-Mei-yu/Mei-yu season (Mayune) but not the post-Mei-yu season (July鈥揂ugust). In a wet monsoon year, the western North Pacific subtropical ridge is stronger as a result of positive feedback that involves the anomalous Hadley and Walker circulations, an atmospheric Rossby wave response to the western Pacific complementary cooling, and the evaporationind feedback. This ridge extends farther to the west from the previous winter to the following fall, resulting in an 850-hPa anomalous anticyclone near the southeast coast of China. This anticyclone 1) blocks the pre-Mei-yu and Mei-yu fronts from moving southward thereby extending the time that the fronts produce stationary rainfall; 2) enhances the pressure gradient to its northwest resulting in a more intense front; and 3) induces anomalous warming of the South China Sea surface through increased downwelling, which leads to a higher moisture supply to the rain area. A positive feedback from the strong monsoon rainfall also appears to occur, leading to an intensified anomalous anticyclone near the monsoon region. This SST ubtropical ridgeonsoon rainfall relationship is observed in both the interannual timescale within each interdecadal period and in the interdecadal scale. The SST anomalies (SSTAs) change sign in northern spring and resemble a tropospheric biennial oscillation (TBO) pattern during the first interdecadal period (1951-77). In the second interdecadal period (1978-96) the sign change occurs in northern fall and the TBO pattern in the equatorial eastern Pacific SST is replaced by longer timescales. This interdecadal variation of the monsoon ST relationship results from the interdecadal change of the background state of the coupled ocean-tmosphere system. This difference gives rise to the different degrees of importance of the feedback from the anomalous circulations near the monsoon region to the equatorial eastern Pacific. In a wet monsoon year, the anomalous easterly winds south of the monsoon-enhanced anomalous anticyclone start to propagate slowly eastward toward the eastern Pacific in May and June, apparently as a result of an atmosphere cean coupled wave motion. These anomalous easterlies carry with them a cooling effect on the ocean surface. In 1951-77 this effect is insignificant as the equatorial eastern Pacific SSTAs, already change from warm to cold in northern spring, probably as a result of negative feedback processes discussed in ENSO mechanisms. In 1978-96 the equatorial eastern Pacific has a warmer mean SST. A stronger positive feedback between SSTA and the Walker circulation during a warm phase tends to keep the SSTA warm until northern fall, when the eastward-propagating anomalous easterly winds reach the eastern Pacific and reverse the SSTA.
    Chen W., J.-K. Park, B. W. Dong, R. Y. Lu, and W.-S. Jung, 2012: The relationship between El Niño and the western North Pacific summer climate in a coupled GCM: Role of the transition of El Niño decaying phases. J. Geophys. Res., 117,D12111, doi: 10.1029/2011JD017385.
    Chen W., J.-Y. Lee, R. Y. Lu, B. W. Dong, and K.-J. Ha, 2015: Intensified impact of tropical Atlantic SST on the western North Pacific summer climate under a weakened Atlantic thermohaline circulation. Climate Dyn., 45, 2033- 2046.10.1007/ tropical North Atlantic (TNA) sea surface temperature (SST) has been identified as one of regulators on the boreal summer climate over the western North Pacific (WNP), in addition to SSTs in the t
    Chen Z. S., Z. P. Wen, R. G. Wu, X. B. Lin, and J. B. Wang, 2015: Relative importance of tropical SST anomalies in maintaining the Western North Pacific anomalous anticyclone during El Niño to La Niña transition years.Climate Dyn., 1- 15.10.1007/ study investigates the relative importance of tropical Indian Ocean warming (IOW) and equatorial central to eastern Pacific cooling (EPC) in sustaining an anomalous Western North Pacific anticyclone (WNPAC) during the transition from an El Nino in the preceding winter to a La Nina in the subsequent summer through a suite of numerical experiments. The numerical results indicate that the WNPAC is maintained by a combined effect of IOW and EPC during the La Nina developing years. The contribution of IOW in maintaining the WNPAC sustains from spring to early summer, but appears to weaken after that as IOW decays. The role of IOW is via an eastward-propagating Kelvin wave induced Ekman divergence mechanism. The decay of IOW is because of reduction in downward solar radiation associated with above normal precipitation in situ. As the cooling develops over central to eastern Pacific from spring to summer, EPC starts to contribute to the maintenance of the WNPAC during summer through stimulating a Rossby wave response to its northwest. In this study, we have identified that the cooling over the central to eastern Pacific plays an important role in sustaining the WNPAC during La Ni甯絘 developing summers. This finding may help improve the prediction of the East Asian summer monsoon, which is closely associated with the WNPAC.
    Choi K.-S., C.-C. Wu, and E.-J. Cha, 2010: Change of tropical cyclone activity by Pacific-Japan teleconnection pattern in the western North Pacific. J. Geophys. Res., 115, D19114.10.1029/[1] This study shows that the Pacific-Japan (PJ) teleconnection pattern has a significant influence on tropical cyclone (TC) activities over the western North Pacific (WNP) during the boreal summer (July, August, and September). During positive (negative) PJ phase, TCs form at a more northward (southward) location, recurve at a more northeastward (southwestward) location, and frequently pass over the northeast Asian (southeast Asian) region, including Korea and Japan (South China Sea and southern China). In particular, this difference in the TC track between the two phases is observed as a dipole-like pattern between the regions of Southeast and Northeast Asia. The TC characteristics during the positive PJ phase are caused by the following two stronger atmospheric circulations over the WNP: an anticyclonic circulation centered to the east of Japan and a cyclonic circulation centered to the east of Taiwan. The southeasterly between these two circulations serves as steering flow that TCs move northward toward Korea and Japan from the northeast of the Philippines. Conversely, TCs during the negative PJ phase mainly move westward toward the South China Sea and southern China by the easterly from a stronger anticyclonic circulation centered to the east of Taiwan. As a result of this feature of TC track during the negative PJ phase, TC lifetime is shorter and TC intensity is weaker.
    Chowdary J. S., S.-P. Xie, J.-Y. Lee, Y. Kosaka, and B. Wang, 2010: Predictability of summer Northwest Pacific climate in 11 coupled model hindcasts: Local and remote forcing. J. Geophys. Res., 115,D22121, doi: 10.1029/2010JD014595.10.1029/[1] The skills of 11 coupled ocean-atmosphere general circulation models (CGCMs) are investigated in the prediction of seasonal rainfall and circulation anomalies over the northwest (NW) Pacific for the period 1980&ndash;2001, with a focus on the summer following the mature phase of El Ni&ntilde;o (hereafter JJA(1)). It is shown that the first empirical orthogonal function (EOF) mode of sea level pressure is closely tied to the second EOF mode of rainfall variability over the NW Pacific during JJA(1), indicative of strong feedback between circulation and convection. Most coupled models and the associated multimodel ensemble well predict these EOF modes and their relationship with high fidelity. Coupled models are capable of predicting suppressed rainfall over the NW Pacific in JJA(1). A few models fail to predict the concurrent weak negative sea surface temperature (SST) anomalies on the southeastern flank of the anomalous anticyclone. This suggests that remote forcing via teleconnections is important for NW Pacific rainfall prediction in those models. In some models, local air-sea interactions seem also to play a role. Specifically, remote forcing by tropical Indian Ocean (TIO) SST variability is identified as influential on NW Pacific climate during JJA(1). TIO SST affects the atmosphere over the NW Pacific by two mechanisms, via the equatorial Kelvin wave and the intensification of the subtropical westerly jet. Overall, models are successful in predicting the antisymmetric patterns of precipitation and winds over TIO during spring, which are critical in sustaining the TIO warming through the subsequent summer.
    Chowdary J. S., S.-P. Xie, J.-J. Luo, J. Hafner, S. Behera, Y. Masumoto, and T. Yamagata, 2011: Predictability of Northwest Pacific climate during summer and the role of the tropical Indian Ocean. Climate Dyn., 36, 607- 621.10.1007/ seasonal forecast system based on a global, fully coupled ocean-tmosphere general circulation model is used to (1) evaluate the interannual predictability of the Northwest Pacific climate during June ugust following El Ni09o [JJA(1)], and (2) examine the contribution from the tropical Indian Ocean (TIO) variability. The model retrospective forecast for 1983-2006 captures major modes of atmospheric variability over the Northwest Pacific during JJA(1), including a rise in sea level pressure (SLP), an anomalous anticyclone at the surface, and a reduction in subtropical rainfall, and increased rainfall to the northeast over East Asia. The anomaly correlation coefficient (ACC) for the leading principal components (PCs) of SLP and rainfall stays above 0.5 for lead time up to 3-402months. The predictability for zonal wind is slightly better. An additional experiment is performed by prescribing the SST climatology over the TIO. In this run, designated as NoTIO, the Northwest Pacific anticyclone during JJA(1) weakens considerably and reduces its westward extension. Without an interactive TIO, the ACC for PC prediction drops significantly. To diagnose the TIO effect on the circulation, the differences between the two runs (Control minus NoTIO) are analyzed. The diagnosis shows that El Nino causes the TIO SST to rise and to remain high until JJA(1). In response to the higher than usual SST, precipitation increases over the TIO and excites a warm atmospheric Kelvin wave, which propagates into the western Pacific along the equator. The decrease in equatorial SLP drives northeasterly wind anomalies, induces surface wind divergence, and suppresses convection over the subtropical Northwest Pacific. An anomalous anticyclone forms in the Northwest Pacific, and the intensified moisture transport on its northwest flank causes rainfall to increase over East Asia. In the NoTIO experiment, the Northwest Pacific anticyclone weakens but does not disappear. Other mechanisms for maintaining this anomalous circulation are discussed.
    Chowdary J. S., S.-P. Xie, H. Tokinaga, Y. M. Okumura, H. Kubota, N. Johnson and X.-T. Zheng, 2012: Interdecadal variations in ENSO teleconnection to the Indo-Western Pacific for 1870-2007. J. Climate, 25, 1722- 1744.10.1175/ Slow modulation of interannual variability and its relationship to El Ni09oouthern Oscillation (ENSO) is investigated for the period of 1870-2007 using shipboard surface meteorological observations along a frequently traveled track across the north Indian Ocean (NIO; from the Gulf of Aden through Malacca Strait) and the South China Sea (to Luzon Strait). During the decades in the late nineteentharly twentieth century and in the late twentieth century, the El Ni09o nduced NIO warming persists longer than during the 1910sid-1970s, well into the summer following the peak of El Ni09o. During the epochs of the prolonged NIO warming, rainfall drops and sea level pressure rises over the tropical northwest Pacific in summer following El Ni09o. Conversely, during the period when the NIO warming dissipates earlier, these atmospheric anomalies are not well developed. This supports the Indian Ocean capacitor concept as a mechanism prolonging El Ni09o influence into summer through the persistent Indian Ocean warming after El Ni09o itself has dissipated. The above centennial modulation of ENSO teleconnection to the Indo orthwest Pacific region is reproduced in an atmospheric general circulation model forced by observed SST. The modulation is correlated not with the Pacific decadal oscillation but rather with the ENSO variance itself. When ENSO is strong, its effect in the Indo orthwest Pacific strengthens and vice versa. The fact that enhanced ENSO teleconnections occurred 100 years ago during the late nineteentharly twentieth century indicates that the recent strengthening of the ENSO correlation over the Indoestern Pacific may not entirely be due to global warming but reflect natural variability.
    Chowdary J. S., C. Gnanaseelan, and S. Chakravorty, 2013: Impact of northwest Pacific anticyclone on the Indian summer monsoon region. Theor. Appl. Climatol., 113, 329- 336.10.1007/ of northwest (NW) Pacific anticyclone on the Indian summer monsoon (ISM), particularly over the head Bay of Bengal and monsoon trough region, is investigated. Strong NW Pacific anticyclone during summer induces negative precipitation anomalies over the head Bay of Bengal and Gangetic Plain region. Westward extension of moisture divergence and dry moisture transport from NW Pacific associated with anticyclone (ridge) and local Hadley cell-induced subsidence are responsible for these negative precipitation anomalies. The impact is maximum when the anticyclone and Indian Ocean basin warming co-occur. This contributes significantly to year-to-year variability of ISM.
    Chowdary, J. S., Coauthors , 2014: Seasonal prediction of distinct climate anomalies in summer 2010 over the tropical Indian Ocean and South Asia. J. Meteor. Soc.Japan, 92, 1- 16.10.2151/ characteristics and predictability of climate anomalies over the tropical Indian Ocean (TIO) and South Asian region during the boreal summer (June-July-August) of 2010 are investigated on the basis of atmospheric regional model simulations and five forecasts obtained from Asia-Pacific Economic Cooperation Climate Center coupled models. The robust features of summer 2010 are the basin-wide TIO warming and enhanced (suppressed) rainfall over the north Indian Ocean and maritime continent (head Bay of Bengal and parts of monsoon trough region). Our regional atmospheric model experiments corroborate that rainfall over South Asia was mostly determined by the TIO sea surface temperature (SST) warming during summer 2010. Most of the coupled models and their multi-model ensemble (MME) used in this study successfully predict the robust features over the TIO and/or South Asian region with 01 May 2010 initial condition. The positive rainfall anomalies over the west coast of India, southern Peninsular India, and central Bay of Bengal are qualitatively well predicted by the MME. Suppressed rainfall over the northeast Bay of Bengal associated with the northwestward extension of the northwest Pacific ridge is also reasonably predicted by the MME. On the other hand, the MME has a moderate skill in predicting positive rainfall anomalies over the convective zone of southeast TIO due to weak local SST warming. Further, the coupled models and their MME fail to predict the anomalous positive rainfall in northern Pakistan because of their inability in predicting mid-latitude circulation anomalies. This study reveals that the predictive skill of rainfall and circulation anomalies during summer 2010 over the TIO and South Asia is largely attributable to the Indian Ocean basin-wide warming during the decay phase of El Nino. These results indicate that the accurate simulation of the TIO SST by coupled models is critical in determining the 2010 South Asian summer monsoon rainfall.
    Christensen, J. H., Coauthors , 2013: Climate phenomena and their relevance for future regional climate change. Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change,T. F. Stocker et al., Eds., Cambridge University Press, 1217-1308, doi: 10.1017/ IPCC assessment reports play an important role in the international climate change negotiation process. The IPCC Fifth Assessment Report (AR5) has been identified as one of the important information sources for the negotiation of a new agreement by the end of 2015 and will have significant influences on the ongoing negotiations on mode of international cooperation to address climate change in the post-2020 period. Based on new and comprehensive observations and advanced model simulations, the newly released IPCC Working Group I (WGI) report reaffirms the fact of global warming trend, strengthens the causality between anthropogenic emissions and global temperature rise and establishes the quantitative relationship between cumulative greenhouse gas emissions and global temperature rise. This paper identifies some key conclusions of the WGI report and analyzes their policy implications, especially their influences on the ongoing negotiation process and the new agreement. It also discusses the role of scientific information in decision-making process, and how this information could be absorbed and used in a scientific manner so that it could better serve the purpose of assisting us in the process of international negotiations and domestic decision making.
    Chu J.-E., K.-J. Ha, J.-Y. Lee, B. Wang, B.-H. Kim, and C. E. Chung, 2014: Future change of the Indian Ocean basin-wide and dipole modes in the CMIP5. Climate Dyn. , 43, 535-
    Diaz H. F., M. P. Hoerling, and J. K. Eischeid, 2001: ENSO variability, teleconnections and climate change.. Int. JClimatol., 21, 1845- 1862.10.1002/ An overview is presented of the principal features of the El Ni&ntilde;o&ndash;Southern Oscillation (ENSO) teleconnections in terms of regional patterns of surface temperature, precipitation and mid-tropospheric atmospheric circulation. The discussion is cast in the context of variations in the associations over time, with decadal scale changes emphasized. In the five decades or so for which we have adequate records to reliably analyse the global aspects of ENSO effects on regional climates around the world, we have witnessed one major decadal scale change in the overall pattern of sea-surface temperatures (SST) in the global ocean, and concomitant changes in the atmospheric response to those changes. The analysis underscores the connection between low frequency changes in tropical SST, ENSO and decadal scale changes in the general atmospheric circulation, pointing to the complex interplay between the canonical ENSO system, slow changes in SST in the Indo-Pacific over the last century, and long-term changes in the atmospheric circulation itself. Published in 2001 by John Wiley & Sons, Ltd.
    Ding H., R. J. Greatbatch, J. Lu, and B. Cash, 2015: The East Asian summer monsoon in pacemaker experiments driven by ENSO. Ocean Dynamics, 65, 385- 393.10.1007/ The variability of the East Asian summer monsoon (EASM) is studied using a pacemaker technique driven by ENSO in an atmospheric general circulation model (AGCM) coupled to a slab mixed layer model. In the pacemaker experiments, sea surface temperature (SST) is constrained to observations in the eastern equatorial Pacific through a q-flux that measures the contribution of ocean dynamics to SST variability, while the AGCM is coupled to the slab model. An ensemble of pacemaker experiments is analyzed using a multivariate EOF analysis to identify the two major modes of variability of the EASM. The results show that the pacemaker experiments simulate a substantial amount (around 45 %) of the variability of the first mode (the Pacific-Japan pattern) in ERA40 from 1979 to 1999. Different from previous work, the pacemaker experiments also simulate a large part (25 %) of the variability of the second mode, related to rainfall variability over northern China. Furthermore, we find that the lower (850 hPa) and the upper (200 hPa) tropospheric circulation of the first mode display the same degree of reproducibility whereas only the lower part of the second mode is reproducible. The basis for the success of the pacemaker experiments is the ability of the experiments to reproduce the observed relationship between El Ni&ntilde;o Southern Oscillation (ENSO) and the EASM.
    Ding Q. H., B. Wang, 2005: Circumglobal teleconnection in the Northern Hemisphere summer. J. Climate, 18, 3483- 3505.10.1175/ of the 56-yr NCEP09CAR reanalysis data reveals a recurrent circumglobal teleconnection (CGT) pattern in the summertime midlatitude circulation of the Northern Hemisphere. This pattern represents the second leading empirical orthogonal function of interannual variability of the upper-tropospheric circulation. The CGT, having a zonal wavenumber-5 structure, is primarily positioned within a waveguide that is associated with the westerly jet stream. The spatial phases of CGT tend to lock to preferred longitudes. The geographically phase-locked patterns bear close similarity during June, August, and September, but the pattern in July shows shorter wavelengths in the North Pacific09orth America sector. The CGT is accompanied by significant rainfall and surface air temperature anomalies in the continental regions of western Europe, European Russia, India, east Asia, and North America. This implies that the CGT may be a source of climate variability and predictability in the above-mentioned midlatitude regions. The CGT has significant correlations with the Indian summer monsoon (ISM) and El Ni01卤o09outhern Oscillation (ENSO). However, in normal ISM years the CGT09NSO correlation disappears; on the other hand, in the absence of El Ni01卤o or La Ni01卤a, the CGT09SM correlation remains significant. It is suggested that the ISM acts as a 0904conductor0909 connecting the CGT and ENSO. When the interaction between the ISM and ENSO is active, ENSO may influence northern China via the ISM and the CGT. Additionally, the variability of the CGT has no significant association with the Arctic Oscillation and the variability of the western North Pacific summer monsoon. The circulation of the wave train shows a barotropic structure everywhere except the cell located to the northwest of India, where a baroclinic circulation structure dominates. Two possible scenarios are proposed. The abnormal ISM may excite an anomalous west-central Asian high and downstream Rossby wave train extending to the North Pacific and North America. On the other hand, a wave train that is excited in the jet exit region of the North Atlantic may affect the west-central Asian high and, thus, the intensity of the ISM. It is hypothesized that the interaction between the global wave train and the ISM heat source may be instrumental in maintaining the boreal summer CGT.
    Ding Q. H., B. Wang, J. M. Wallace, and G. Branstator, 2011: Tropical-extratropical teleconnections in boreal summer: Observed interannual variability. J. Climate, 24, 1878-
    Ding Y. H., J. C. L. Chan, 2005: The East Asian summer monsoon: an overview. Meteor. Atmos. Phys., 89, 117- 142.10.1007/ present paper provides an overview of major problems of the East Asian summer monsoon. The summer monsoon system over East Asia (including the South China Sea (SCS)) cannot be just thought of as the eastward and northward extension of the Indian monsoon. Numerous studies have well documented that the huge Asian summer monsoon system can be divided into two subsystems: the Indian and the East Asian monsoon system which are to a greater extent independent of each other and, at the same time, interact with each other. In this context, the major findings made in recent two decades are summarized below: (1) The earliest onset of the Asian summer monsoon occurs in most of cases in the central and southern Indochina Peninsula. The onset is preceded by development of a BOB (Bay of Bengal) cyclone, the rapid acceleration of low-level westerlies and significant increase of convective activity in both areal extent and intensity in the tropical East Indian Ocean and the Bay of Bengal. (2) The seasonal march of the East Asian summer monsoon displays a distinct stepwise northward and northeastward advance, with two abrupt northward jumps and three stationary periods. The monsoon rain commences over the region from the Indochina Peninsula-the SCS-Philippines during the period from early May to mid-May, then it extends abruptly to the Yangtze River Basin, and western and southern Japan, and the southwestern Philippine Sea in early to mid-June and finally penetrates to North China, Korea and part of Japan, and the topical western West Pacific. (3) After the onset of the Asian summer monsoon, the moisture transport coming from Indochina Peninsula and the South China Sea plays a crucial witch role in moisture supply for precipitation in East Asia, thus leading to a dramatic change in climate regime in East Asia and even more remote areas through teleconnection. (4) The East Asian summer monsoon and related seasonal rain belts assumes significant variability at intraseasonal, interannual and interdecadal time scales. Their interaction, i.e., phase locking and in-phase or out-phase superimposing, can to a greater extent control the behaviors of the East Asian summer monsoon and produce unique rythem and singularities. (5) Two external forcing i.e., Pacific and Indian Ocean SSTs and the snow cover in the Eurasia and the Tibetan Plateau , are believed to be primary contributing factors to the activity of the East Asian summer monsoon. However, the internal variability of the atmospheric circulation is also very important. In particular, the blocking highs in mid-and high latitudes of Eurasian continents and the subtropical high over the western North Pacific play a more important role which is quite different from the condition for the South Asian monsoon. The later is of tropical monsoon nature while the former is of hybrid nature of tropical and subtropical monsoon with intense impact from mid-and high latitudes.
    Du Y., S.-P. Xie, 2008: Role of atmospheric adjustments in the tropical Indian Ocean warming during the 20th century in climate models. Geophys. Res. Lett., 35,L08712, doi: 10.1029/ 2008GL033631.10.1029/ tropical Indian Ocean has been warming steadily since 1950s, a trend simulated by a large ensemble of climate models. In models, changes in net surface heat flux are small and the warming is trapped in the top 125 m depth. Analysis of the model output suggests the following quasi-equilibrium adjustments among various surface heat flux components. The warming is triggered by the greenhouse gas-induced increase in downward longwave radiation, amplified by the water vapor feedback and atmospheric adjustments such as weakened winds that act to suppress turbulent heat flux from the ocean. The sea surface temperature dependency of evaporation is the major damping mechanism. The simulated changes in surface solar radiation vary considerably among models and are highly correlated with inter-model variability in SST trend, illustrating the need to reduce uncertainties in cloud simulation.
    Du Y., S.-P. Xie, G. Huang, and K. M. Hu, 2009: Role of air-sea interaction in the long persistence of El Niño-induced north Indian Ocean warming. J. Climate, 22, 2023- 2038.10.1175/ El Ni09o induces a basin-wide increase in tropical Indian Ocean (TIO) sea surface temperature (SST) with a lag of one season. The north IO (NIO), in particular, displays a peculiar double-peak warming with the second peak larger in magnitude and persisting well through the summer. Motivated by recent studies suggesting the importance of the TIO warming for the Northwest Pacific and East Asian summer monsoons, the present study investigates the mechanisms for the second peak of the NIO warming using observations and general circulation models. This analysis reveals that internal air鈥搒ea interaction within the TIO is key to sustaining the TIO warming through summer. During El Ni09o, anticyclonic wind curl anomalies force a downwelling Rossby wave in the south TIO through Walker circulation adjustments, causing a sustained SST warming in the tropical southwest IO (SWIO) where the mean thermocline is shallow. During the spring and early summer following El Ni09o, this SWIO warming sustains an antisymmet...
    Du Y., L. Yang, and S.-P. Xie, 2011: Tropical Indian Ocean influence on Northwest Pacific tropical cyclones in summer following strong El Niño. J. Climate, 24, 315- 322.
    Du Y., S.-P. Xie, Y. L. Yang, X. T. Zheng, L. Liu, and G. Huang, 2013: Indian Ocean variability in the CMIP5 multimodel ensemble: The Basin mode. J. Climate, 26, 7240- 7266.10.1175/ This study evaluates the simulation of the Indian Ocean Basin (IOB) mode and relevant physical processes in models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). Historical runs from 20 CMIP5 models are available for the analysis. They reproduce the IOB mode and its close relationship to El Ni09o–Southern Oscillation (ENSO). Half of the models capture key IOB processes: a downwelling oceanic Rossby wave in the southern tropical Indian Ocean (TIO) precedes the IOB development in boreal fall and triggers an antisymmetric wind anomaly pattern across the equator in the following spring. The anomalous wind pattern induces a second warming in the north Indian Ocean (NIO) through summer and sustains anticyclonic wind anomalies in the northwest Pacific by radiating a warm tropospheric Kelvin wave. The second warming in the NIO is indicative of ocean–atmosphere interaction in the interior TIO. More than half of the models display a double peak in NIO warming, as observed following El Ni09o, while the rest show only one winter peak. The intermodel diversity in the characteristics of the IOB mode seems related to the thermocline adjustment in the south TIO to ENSO-induced wind variations. Almost all the models show multidecadal variations in IOB variance, possibly modulated by ENSO.
    Enomoto T., 2004: Interannual variability of the Bonin high associated with the propagation of Rossby waves along the Asian jet. J. Meteor. Soc.Japan, 82, 1019- 1034.10.2151/ variability of the Ogasawara (Bonin) high in August is examined in relation to propagation of stationary Rossby waves along the Asian jet using monthly averages from the NCEP/NCAR reanalysis dataset for 52 years. The perturbation kinetic energy at 200 hPa is used as a measure of the activity of stationary Rossby waves along the Asian jet. Composite maps of five relatively wavy-jet years with close phases show an enhanced anticyclone over Japan. This anomalous ridge has a maximum amplitude at 250 hPa and extends throughout the troposphere with little zonal and slight northward tilts. Wave-activity and isentropic potential vorticity analyses clearly show that the ridge is created by the propagation of stationary Rossby waves to Japan. The anomalous ridge accompanies a positive temperature anomaly over Japan in the entire troposphere. A negative temperature anomaly to the east of Japan is also created in the lower troposphere by the northerly flow between the anomalous ridge and trough. By contrast, the equivalent-barotropic ridge over Japan is very weak in the zonal-jet years. Although Rossby waves are as strong as those in the wavy-jet years near the source, they are found to converge to the southeast of its source with little further downstream propagation. This contrast in the behaviour of Rossby waves is consistent with the intensity of the Asian jet to the east of 90掳E. The composite analysis suggests that the enhancement of a deep ridge near Japan is regulated by the intensity of the Asian jet. The composite analysis study conducted here emphasizes the importance of the propagation of stationary Rossby waves along the Asian jet for the late summer climate in northeastern Asia.
    Feng J., W. Chen, C. Y. Tam, and W. Zhou, 2011: Different impacts of El Niño and El Niño Modoki on China rainfall in the decaying phases. Int. J. Climatol., 31, 2091- 2101.
    Feng J., L. Wang, and W. Chen, 2014: How does the East Asian summer monsoon behave in the decaying phase of El Niño during different PDO phases? J. Climate, 27, 2682- 2698.10.1175/ Modulation of the Pacific decadal oscillation (PDO) on the behavior of the East Asian summer monsoon (EASM) in El Ni&ntilde;o decaying years has been studied. When El Ni&ntilde;o is in phase with the PDO (El Ni&ntilde;o/high PDO), the low-level atmospheric anomalies are characterized by an anticyclone around the Philippines and a cyclone around Japan, inducing an anomalous tripolar rainfall pattern in China. In this case, the western Pacific subtropical high (WPSH) experiences a one-time slightly northward shift in July and then stays stationary from July to August. The corresponding anomalous tripolar rainfall pattern has weak subseasonal variations. When El Ni&ntilde;o is out of phase with the PDO (El Ni&ntilde;o/low PDO), however, the anomalous Philippines anticyclone has a much larger spatial domain, thereby causing an anomalous dipole rainfall pattern. Accordingly, WPSH experiences clearly two northward shifts. Therefore, the related dipole rainfall pattern has large subseasonal variations. One pronounced feature is that the positive rainfall anomalies shift northward from southern China in June to central China in July and finally to northern China in August. The different El Ni&ntilde;o&ndash;EASM relationships are caused by the influences of PDO on the decaying speed of El Ni&ntilde;o. During the high PDO phase, El Ni&ntilde;o decays slowly and has a strong anchor in the north Indian Ocean warming, which is responsible for the anomalous EASM. Comparatively, during the low PDO phase, El Ni&ntilde;o decays rapidly and La Ni&ntilde;a develops in summer, which induces different EASM anomalies from that during the high PDO phase. Additionally, PDO changes El Ni&ntilde;o behaviors mainly via modifying the background tropical winds.
    Gill A. E., 1980: Some simple solutions for heat-induced tropical circulation. Quart. J. Roy. Meteor. Soc., 106, 447- 462.10.1002/ A simple analytic model is constructed to elucidate some basic features of the response of the tropical atmosphere to diabatic heating. In particular, there is considerable east-west asymmetry which can be illustrated by solutions for heating concentrated in an area of finite extent. This is of more than academic interest because heating in practice tends to be concentrated in specific areas. For instance, a model with heating symmetric about the equator at Indonesian longitudes produces low-level easterly flow over the Pacific through propagation of Kelvin waves into the region. It also produces low-level westerly inflow over the Indian Ocean (but in a smaller region) because planetary waves propagate there. In the heating region itself the low-level flow is away from the equator as required by the vorticity equation. The return flow toward the equator is farther west because of planetary wave propagation, and so cyclonic flow is obtained around lows which form on the western margins of the heating zone. Another model solution with the heating displaced north of the equator provides a flow similar to the monsoon circulation of July and a simple model solution can also be found for heating concentrated along an inter-tropical convergence line.
    Han W. Q., J. Vialard, M. J. McPhaden, T. Lee, Y. Masumoto, M. Feng, and W. P. M. de Ruijter, 2014: Indian Ocean decadal variability: A review. Bull. Amer. Meteor. Soc.,95, 1679-1703, doi: 10.1175/
    Harrison D. E., N. K. Larkin, 1996: The COADS Sea level pressure signal: A near-global El Niño composite and time series view, 1946-1993. J. Climate, 9, 3025- 3055.10.1175/1520-0442(1996)0092.0.CO; Using COADS data for the period 1946–1993, the near-global sea level pressure (SLP) patterns associated with interannual variability and the climatological seasonal march are discussed. A particular focus concerns the patterns associated with the two years before and after the South American sea surface temperatures rise (El Ni09o). The ten El Ni09o events in this record are composited, and the robustness of the features of this composite is tested. Many features of the composite are quite robust; they occur during most El Ni09o events and are infrequent during non-El Ni09o periods. The most robust feature is an area of negative SLP anomaly (SLPA) in the eastern equatorial Pacific during Year(0) of the composite. This feature exceeds significance thresholds during every El Ni09o year and never during non-El Ni09o years; it correlates better with central Pacific SST variability than does the SOI. A west-central North Pacific positive SLPA, occurring late in Year(0) and lasting into the spring of year (+1) is the second most robust feature. Strong SLPA signals occur in the eastern South Pacific and around Australia in many events, but the behavior varies greatly from event to event. Some events show interesting signals in the Indian and Atlantic Oceans, but the behavior is not sufficiently general to be a statistically meaningful element of the composite. The largest signals in the composite occur in the eastern equatorial and west-central North Pacific and not in the Southern Hemisphere. Thus, the large-scale SLP variations associated with El Ni09o periods are not dominated by the classical Southern Oscillation. Little evidence is found for phase propagation of the signal in El Niflo years. Although several features of the composite occur during the same season in each El Ni09o period, so that the main signals are “phase locked” to the seasonal cycle, the patterns of variability have little in common with the patterns of the seasonal march of SLP.
    Hirota N., M. Takahashi, 2012: A tripolar pattern as an internal mode of the East Asian summer monsoon. Climate Dyn., 39, 2219- 2238.10.1007/ tripolar anomaly pattern with centers located around the Philippines, China/Japan, and East Siberia dominantly appears in climate variations of the East Asian summer monsoon. In this study, we extracted this pattern as the first mode of a singular value decomposition (SVD1) over East Asia. The squared covariance fraction of SVD1 was 59聽%, indicating that this pattern can be considered a dominant pattern of climate variations. Moreover, the results of numerical experiments suggested that the structure is also a dominant pattern of linear responses, even if external forcing is distributed homogeneously over the Northern Hemisphere. Thus, the tripolar pattern can be considered an internal mode that is characterized by the internal atmospheric processes. In this pattern, the moist processes strengthen the circulation anomalies, the dynamical energy conversion supplies energy to the anomalies, and the Rossby waves propagate northward in the lower troposphere and southeastward in the upper troposphere. These processes are favorable for the pattern to have large amplitude and to influence a large area.
    Hong C.-C., T.-C. Chang, and H.-H. Hsu, 2014: Enhanced relationship between the tropical Atlantic SST and the summertime western North Pacific subtropical high after the early 1980s. J. Geophys. Res., 119, 3715- 3722.10.1002/ The western North Pacific subtropical high (WNPSH) in boreal summer shows a remarkable enhancement after the early 1980s. Whereas the sea surface temperature (SST) in the North Indian Ocean (NIO) and the equatorial eastern Pacific had been noted to have remarkable local or remote effects on enhancing the WNPSH, the influence of the Atlantic SST, so far, is hardly explored. This article reports a new finding: enhanced relationship between the tropical Atlantic (TA)-SST and the WNPSH after the early 1980s. Regression study suggests that the warm TA-SST produced a zonally overturning circulation anomaly, with descending over the equatorial central Pacific and ascending over the tropical Atlantic/eastern Pacific. The anomalous descending over the equatorial central Pacific likely induced low-level anticyclonic anomaly to the west and therefore enhanced the WNPSH. One implication of this new finding is for predictability. The well-known “spring predictability barrier” (i.e., the influence of El Ni09o–Southern Oscillation (ENSO) falls dramatically during boreal spring) does not apply to the TA-SST/WNPSH relationship. The TA-SST shows consistently high correlation starting from boreal spring when the ENSO influence continues declining. The TA-SST extends the predictability of the WNPSH in boreal summer approximately one season earlier to boreal spring.
    Horel J. D., J. M. Wallace, 1981: Planetary-scale atmospheric phenomena associated with the Southern oscillation. Mon. Wea. Rev., 109, 813-
    Hoskins B. J., D. J. Karoly, 1981: The steady linear response of a spherical atmosphere to thermal and orographic forcing. J. Atmos. Sci., 38, 1179- 1196.10.1175/1520-0469(1981)0382.0.CO; Motivated by some results from barotropic models, a linearized steady-state five-layer baroclinic model is used to study the response of a spherical atmosphere to thermal and orographic forcing. At low levels the significant perturbations are confined to the neighborhood of the source and for midlatitude thermal forcing these perturbations are crucially dependent on the vertical distribution of the source. In the upper troposphere the sources generate wavetrains which are very similar to those given by barotropic models. For a low-latitude source, long wavelengths propagate strongly polewards as well as eastwards. Shorter wavelengths are trapped equatorward of the poleward flank of the jet, resulting in a split of the wave-trains at this latitude. Using reasonable dissipation magnitudes, the easiest way to produce an appreciable response in middle and high latitudes is by subtropical forcing. These results suggest an explanation for the shapes of patterns described in observational studies. The theory for waves propagating in a slowly varying medium is applied to Rossby waves propagating in a barotropic atmosphere. The slow variation of the medium is associated with the sphericity of the domain and the latitudinal structure of the zonal wind. Rays along which wave activity propagates, the speeds of propagation, and the amplitudes and phases along these rays are determined for a constant angular velocity basic flow as well as a more realistic jet flow. They agree well with the observational and numerical model results and give a simple interpretation of them.
    Houze R. A., Jr., K. L. Rasmussen, S. Medina, S. R. Brodzik, and U. Romatschke, 2011: Anomalous atmospheric events leading to the Summer 2010 floods in Pakistan. Bull. Am. Meteor. Soc., 92, 291- 298.10.1175/ abstract available.
    Hu K. M., G. Huang, and R. H. Huang, 2011: The impact of tropical Indian Ocean variability on summer surface air temperature in China. J. Climate, 24, 5365- 5377.10.1175/ Evidence is presented that the boreal summer surface air temperature over south China and northeast China is remotely influenced by the Indian Ocean Basin mode (IOBM) sea surface temperature (SST) anomalies. Above-normal temperature in south China and below-normal temperature in northeast China correspond to a simultaneous Indian Ocean Basin warming. The teleconnection from Indian Ocean SST anomalies to China summer surface air temperature is investigated using observations and an atmospheric general circulation model (AGCM). The results herein indicate that the tropical Indian Ocean Basin warming can trigger a low-level anomalous anticyclone circulation in the subtropical northwest Pacific and an anomalous cyclone circulation in midlatitude East Asia through emanating a baroclinic Kelvin wave. In south China, the reduced rainfall and downward vertical motion associated with the anomalous low-level anticyclone circulation lead to above-normal summer surface air temperature. In northeast China, by contrast, upward vertical motion associated with the anomalous cyclone leads to below-normal summer surface air temperature.
    Hu K. M., G. Huang, X. Qu, and R. H. Huang, 2012: The Impact of Indian Ocean variability on high temperature extremes across the southern Yangtze River Valley in late summer. Adv. Atmos. Sci.,29, 91-100, doi: 10.1007/s00376-011-0209-2.
    Hu K. M., G. Huang, X.-T. Zheng, S.-P. Xie, X. Qu, Y. Du, and L. Liu, 2014: Interdecadal variations in ENSO influences on Northwest Pacific-East Asian early summertime climate simulated in CMIP5 models. J. Climate, 27, 5982- 5998.ffd1286f-51aa-4f38-86cf-6aba304f8214
    Huang G., K. M. Hu, and S.-P. Xie, 2010: Strengthening of tropical Indian Ocean teleconnection to the Northwest Pacific since the Mid-1970s: An atmospheric GCM study. J. Climate, 23, 5294- 5304.10.1175/ The correlation of northwest (NW) Pacific climate anomalies during summer with El Ni09o–Southern Oscillation (ENSO) in the preceding winter strengthens in the mid-1970s and remains high. This study investigates the hypothesis that the tropical Indian Ocean (TIO) response to ENSO is key to this interdecadal change, using a 21-member ensemble simulation with the Community Atmosphere Model, version 3 (CAM3) forced by the observed history of sea surface temperature (SST) for 1950–2000. In the model hindcast, the TIO influence on the summer NW Pacific strengthens in the mid-1970s, and the strengthened TIO teleconnection coincides with an intensification of summer SST variability over the TIO. This result is corroborated by the fact the model’s skills in simulating NW Pacific climate anomalies during summer increase after the 1970s shift. During late spring to early summer, El Ni09o–induced TIO warming decays rapidly for the epoch prior to the 1970s shift but grows and persists through summer for the epoch occurring after it. This difference in the evolution of the TIO warming determines the strength of the TIO teleconnection to the NW Pacific in the subsequent summer. An antisymmetric wind pattern develops in spring across the equator over the TIO, and the associated northeasterly anomalies aid the summer warming over the north Indian Ocean by opposing the prevailing southwest monsoon. In the model, this antisymmetric spring wind pattern is well developed after but absent before the 1970s shift.
    Huang R. H., F. Sun, 1992: Impact of the tropical western Pacific on the East Asian summer monsoon. J. Meteor. Soc.Japan, 70, 213- 256.
    Huang R. H., Y. F. Wu, 1989: The influence of ENSO on the summer climate change in China and its mechanism. Adv. Atmos. Sci.,6, 21-32, doi: 10.1007/BF02656915.10.1007/ influence of ENSO on the summer climate change in China and its mechanism from the observed data is discussed. It is discovered that in the developing stage of ENSO, the SST in the western tropical Pacific is colder in summer, the convective activities may be weak around the South China Sea and the Philippines. As a consequence, the subtropical high shifted southward. Therefore, a drought may be caused in the Indo-China peninsula and in the South China. Moreover, in midsummer the subtropical high is weak over the Yangtze River valley and Huaihe River valley, and the flood may be caused in the area from the Yangtze River valley to Huaihe River valley. On the contrary, in the decaying stage of ENSO. the convective activities may be strong around the Philippines, and the subtropical high shifted northward, a drought may be caused in the Yangtze River valley and Huaihe River valley.
    Huang R. H., W. Chen, B. L. Yang, and R. H. Zhang, 2004: Recent advances in studies of the interaction between the East Asian winter and summer monsoons and ENSO cycle. Adv. Atmos. Sci.,21, 407-424, doi: 10.1007/BF02915568.10.1007/ advances in studies on the interaction between the East Asian monsoon and the ENSO cycle are reviewed in this paper. Through the recent studies, not only have the responding features and processes of the East Asian winter and summer monsoon circulation anomalies and summer rainfall anomalies in East Asia to the ENSO cycle during its different stages been understood further, but also have the thermal and dynamic effects of the tropical western Pacific on the ENSO cycle been deeply analyzed from the observational facts and dynamic theories. The results of observational and theoretical studies showed that the dynamical effect of the atmospheric circulation and zonal wind anomalies in the lower troposphere over the tropical western Pacific on the ENSO cycle may be through the excitation of the equatorial oceanic Kelvin wave and Rossby waves in the equatorial Pacific. These studies demonstrated further that the ENSO cycle originates from the tropical western Pacific. Moreover, these recent studies also showed that the atmospheric circulation and zonal wind anomalies over the tropical western Pacific not only result from the air-sea interaction over the tropical western Pacific, but are also greatly influenced by the East Asian winter and summer monsoons. Additionally, the scientific problems in the interaction between the Asian monsoon and the ENSO cycle which should be studied further in the near future are also pointed out in this paper.
    Hsu H.-H., S.-M. Lin, 2007: Asymmetry of the tripole rainfall pattern during the East Asian summer. J. Climate, 20, 4443-4458, doi: 10.1175/
    Izumo T., C. B. Montègut, J.-J. Luo, S. K. Behera, S. Masson, and T. Yamagata, 2008: The role of the western Arabian Sea upwelling in Indian monsoon rainfall variability. J. Climate, 21, 5603-;link_type=DOI
    Jiang X. W., S. Yang, J. P. Li, Y. Q. Li, H. R. Hu, and Y. Lian, 2013: Variability of the Indian Ocean SST and its possible impact on summer western North Pacific anticyclone in the NCEP climate forecast system. Climate Dyn.,41, 2199-2212, doi: 10.1007/s00382-013-1934-2.10.1007/ NCEP Climate Forecast System version 2 (CFSv2) provides important source of information about the seasonal prediction of climate over the Indo-Pacific oceans. In this study, the authors provide a comprehensive assessment of the prediction of sea surface temperature (SST) in the tropical Indian Ocean (IO). They also investigate the impact of tropical IO SST on the summer anomalous anticyclonic circulation over the western North Pacific (WNPAC), focusing on the relative contributions of local SST and remote forcing of tropical IO SST to WNPAC variations. The CFSv2 captures the two most dominant modes of summer tropical IO SST: the IO basin warming (IOBW) mode and the IO dipole (IOD) mode, as well as their relationship with El Nino-Southern Oscillation (ENSO). However, it produces a cold SST bias in IO, which may be attributed to deeper-than-observed mixed layer and smaller-than-observed total downward heat flux in the tropical IO. It also overestimates the correlations of ENSO with IOBW and IOD, but underestimates the magnitude of IOD and summer IOBW. The CFSv2 captures the climate anomalies related to IOBW but not those related to IOD. It depicts the impact of summer IOBW on WNPAC via the equatorial Kelvin wave, which contributes to the maintenance of WNPAC in July and August. The WNPAC in June is mostly forced by local cold SST, which is better predicted by the CFSv2 compared to July and August. The mechanism for WNPAC maintenance may vary with lead time in the CFSv2.
    Kawamura R., T. Matsuura, S. Iizuka, 2001: Role of equatorially asymmetric sea surface temperature anomalies in the Indian Ocean in the Asian summer monsoon and El Niño-Southern oscillation coupling. J. Geophys. Res., 106( D5), 4681- 4693.
    Kent E. C., S. D. Woodruff, and D. I. Berry, 2007: Metadata from WMO publication No. 47 and an assessment of Voluntary observing ship observation heights in ICOADS. J. Atmos. Oceanic Technol., 24, 214-
    Kim J.-S., R. C.-Y. Li, and W. Zhou, 2012: Effects of the Pacific-Japan teleconnection pattern on tropical cyclone activity and extreme precipitation events over the Korean peninsula. J. Geophys. Res., 117, D18109.10.1029/ Top of page Abstract 1.Introduction 2.Data and Methodology 3.Characteristics of WNP TC Activity Associated With the PJ Pattern 4.TC-Induced Precipitation Variability Associated With PJ Phases 5.Summary and Conclusions Acknowledgments References Supporting Information [1] In this study, an exploratory analysis was carried out to gain a better understanding of the potential impacts of the two phases (negative and positive) of the Pacific-Japan (PJ) pattern on tropical cyclone (TC) activity affecting the Korean Peninsula (KP) and TC-induced extreme precipitation events over five major river basins in Korea. The results show that large-scale atmospheric environments during the years in the positive PJ phase (referred to as positive PJ years) are more favorable for TC activity than those during the years in the negative PJ phase (referred to as negative PJ years). It is found that wind shear is weaker, rising motion is stronger, and relative humidity is higher over the KP in positive PJ years than in negative PJ years. TCs affecting the KP during positive (negative) PJ years tend to occur more to the southwest (northeast), recurve at locations more to the northwest (northeast), and show an increase (decrease) in frequency over Korea and Japan. As a result, TCs making landfall are found more often over southeastern South Korea during positive PJ years. Despite the relatively modest sample size used in this study, we expect that the results described herein will be useful in developing a critical support system for the effective reduction and mitigation of TC-caused disasters as well as for water supply management in coupled human and natural systems.
    Klein S. A., B. J. Soden, and N.-C. Lau, 1999: Remote sea surface temperature variations during ENSO: Evidence for a tropical atmospheric bridge. J. Climate, 12, 917-
    Kobayashi, S., Coauthors , 2015: The JRA-55 Reanalysis: General specifications and basic characteristics. J. Meteor. Soc.Japan, 93, 5- 48.10.2151/ Japan Meteorological Agency (JMA) conducted the second Japanese global atmospheric reanalysis, called the Japanese 55-year Reanalysis or JRA-55. It covers the period from 1958, when regular radiosonde observations began on a global basis. JRA-55 is the first comprehensive reanalysis that has covered the last half-century since the European Centre for Medium-Range Weather Forecasts 45-year Reanalysis (ERA-40), and is the first one to apply four-dimensional variational analysis to this period. The main objectives of JRA-55 were to address issues found in previous reanalyses and to produce a comprehensive atmospheric dataset suitable for studying multidecadal variability and climate change. This paper describes the observations, data assimilation system, and forecast model used to produce JRA-55 as well as the basic characteristics of the JRA-55 product. RA-55 has been produced with the TL319 version of JMA operational data assimilation system as of December 2009, which was extensively improved since the Japanese 25-year Reanalysis (JRA-25). It also uses several newly available and improved past observations. The resulting reanalysis products are considerably better than the JRA-25 product. Two major problems of JRA-25 were a cold bias in the lower stratosphere, which has been diminished, and a dry bias in the Amazon basin, which has been mitigated. The temporal consistency of temperature analysis has also been considerably improved compared to previous reanalysis products. Our initial quality evaluation revealed problems such as a warm bias in the upper troposphere, large upward imbalance in the global mean net energy fluxes at the top of the atmosphere and at the surface, excessive precipitation over the tropics, and unrealistic trends in analyzed tropical cyclone strength. This paper also assesses the impacts of model biases and changes in the observing system, and mentions efforts to further investigate the representation of low-frequency variability and trends in JRA-55.
    Kosaka Y., H. Nakamura, 2006: Structure and dynamics of the summertime Pacific-Japan teleconnection pattern. Quart. J. Roy. Meteor. Soc., 132, 2009- 2030.
    Kosaka Y., H. Nakamura, 2010: Mechanisms of meridional teleconnection observed between a summer monsoon system and a subtropical anticyclone. Part I: The Pacific-Japan pattern. J. Climate, 23, 5085- 5108.
    Kosaka Y., H. Nakamura, M. Watanabe, and M. Kimoto, 2009: Analysis on the dynamics of a wave-like teleconnection pattern along the summertime Asian jet based on a reanalysis dataset and climate model simulations. J. Meteor. Soc.Japan, 87, 561- 580.10.2151/ Silk Road pattern, a wave-like anomaly pattern observed along the summertime Asian jet, is one of the major teleconnection patterns that can influence the East Asian summertime climate. Our analysis based on a reanalysis (JRA-25) dataset confirms the conventional notion that the pattern has a characteristic of a free stationary Rossby wave train, with its horizontal wavenumber close to the stationary Rossby wavenumber determined by the mean intensity of the jet. However, our analysis reveals its more essential characteristic as a dynamical mode whose extraction of available potential energy from the baroclinic Asian jet is highly efficient for its self-maintenance. Our analysis also reveals high sensitivity of its barotropic energy conversion to subtle zonal asymmetries of the Asian jet, which can be regarded as a critical factor to anchor the strongest vorticity anomaly around the western jet core and thereby determine the preferred longitudinal phase alignment of the wave train as observed. In fact, singular value decomposition of a global baroclinic model linearized about the observed mean state for boreal summer leads to identification of a perturbation similar to the Silk Road pattern with respect to its structure and energetics. It is thus indicated that the configuration of the mean flow determines the dominant phase, as well as the meridional location and the wavenumber, of the Silk Road pattern.The aforementioned dynamical characteristics of the Silk Road pattern are found useful for assessing and interpreting the reproducibility of the pattern in the present-day climate simulated in climate models that participated in the phase 3 of the Coupled Model Intercomparison Project (CMIP3). The pattern tends to be identified as the dominant mode of upper-tropospheric meridional wind variability as observed in such models that can reproduce the mean Asian jet realistically, including its zonal structure, which confirms the dynamics of the Silk Road pattern revealed in our observational analysis. On the basis of our analysis, a metric is proposed for assessing the models' reproducibility of the pattern.
    Kosaka Y., S.-P. Xie, and H. Nakamura, 2011: Dynamics of interannual variability in summer precipitation over East Asia. J. Climate, 24, 5435- 5453.10.1175/ The summertime mei-yu–baiu rainband over East Asia displays considerable interannual variability. A singular value decomposition (SVD) analysis for interannual variability reveals that precipitation anomalies over the mei-yu–baiu region are accompanied by in situ anomalies of midtropospheric horizontal temperature advection. Anomalous warm (cool) advection causes increased (decreased) mei-yu–baiu precipitation locally by inducing adiabatic ascent (descent). The anomalous precipitation acts to reinforce the vertical motion, forming a feedback system. By this mechanism, the remotely forced anomalous atmospheric circulation can induce changes in mei-yu–baiu precipitation. The quasi-stationary precipitation anomalies induced by this mechanism are partially offset by transient eddies. The SVD analysis also reveals the association of mei-yu–baiu precipitation anomalies with several teleconnection patterns, suggesting remote induction mechanisms. The Pacific–Japan (PJ) teleconnection pattern, which is associated with anomalous convection over the tropical western North Pacific, contributes to mei-yu–baiu precipitation variability throughout the boreal summer. The PJ pattern mediates influences of the El Ni09o–Southern Oscillation in preceding boreal winter on mei-yu–baiu precipitation. In early summer, the leading covariability pattern between precipitation and temperature advection also features the Silk Road pattern—a wave train along the summertime Asian jet—and another wave train pattern to the north along the polar-front jet that often leads to the development of the surface Okhotsk high.
    Kosaka Y., J. S. Chowdary, S.-P. Xie, Y.-M. Min, and J.-Y. Lee, 2012: Limitations of seasonal predictability for summer climate over East Asia and the Northwestern Pacific. J. Climate, 25, 7574- 7589.10.1175/ Predictability of summer climate anomalies over East Asia and the northwestern Pacific is investigated using observations and a multimodel hindcast ensemble initialized on 1 May for the recent 20-30 yr. Summertime East Asia is under the influence of the northwestern Pacific subtropical high (PASH). The Pacific-Japan (PJ) teleconnection pattern, a meridional dipole of sea level pressure variability, affects the northwestern PASH. The forecast models generally capture the association of the PJ pattern with the El Nino-Southern Oscillation (ENSO). The Silk Road pattern, a wave train along the summer Asian jet, is another dominant teleconnection that influences the northwestern PASH and East Asia. In contrast to the PJ pattern, observational analysis reveals a lack of correlations between the Silk Road pattern and ENSO. Coupled models cannot predict the temporal phase of the Silk Road pattern, despite their ability to reproduce its spatial structure as the leading mode of atmospheric internal variability. Thus, the pattern is rather unpredictable at monthly to seasonal lead, limiting the seasonal predictability for summer in East Asia. The anomalous summer of 2010 in East Asia is a case in point, illustrating the interference by the Silk Road pattern. Canonical anomalies associated with a decayed El Nino and developing La Nina would have the PJ pattern bring a cold summer to East Asia in 2010. In reality, the Silk Road pattern overwhelmed this tendency, bringing a record-breaking hot summer instead. A dynamical model experiment indicates that European blocking was instrumental in triggering the Silk Road pattern in the 2010 summer.
    Kosaka Y., S.-P. Xie, N.-C. Lau, and G. A. Vecchi, 2013: Origin of seasonal predictability for summer climate over the Northwestern Pacific. Proceedings of the National Academy of Sciences of the United States of America, 110, 7574- 7579.10.1073/ Summer climate in the Northwestern Pacific (NWP) displays large year-to-year variability, affecting densely populated Southeast and East Asia by impacting precipitation, temperature, and tropical cyclones. The Pacific-Japan (PJ) teleconnection pattern provides a crucial link of high predictability from the tropics to East Asia. Using coupled climate model experiments, we show that the PJ pattern is the atmospheric manifestation of an air-sea coupled mode spanning the Indo-NWP warm pool. The PJ pattern forces the Indian Ocean (IO) via a westward propagating atmospheric Rossby wave. In response, IO sea surface temperature feeds back and reinforces the PJ pattern via a tropospheric Kelvin wave. Ocean coupling increases both the amplitude and temporal persistence of the PJ pattern. Cross-correlation of ocean-atmospheric anomalies confirms the coupled nature of this PJIO mode. The ocean-atmosphere feedback explains why the last echoes of El Nino-Southern Oscillation are found in the IO-NWP in the form of the PJIO mode. We demonstrate that the PJIO mode is indeed highly predictable; a characteristic that can enable benefits to society.
    Kubota H., Y. Kosaka, and S.-P. Xie, 2015: A 117-year long index of the Pacific-Japan pattern with application to interdecadal variability. Int. J. Climatol., doi: 10.1002/joc.4441.
    Kug J.-S., I.-S. Kang, 2006: Interactive feedback between ENSO and the Indian Ocean. J. Climate, 19, 1784-1801, doi: 10.1175/
    Kurihara K., T. Tsuyuki, 1987: Development of the barotropic high around Japan and its association with Rossby wave-like propagations over the North Pacific: Analysis of August 1984. J. Meteor. Soc.Japan, 65, 237- 246.10.1175/1520-0469(1987)044<1106:OOTISF>2.0.CO; works with energy balance climate models and oceanic general circulation models have assessed the potential role of the world ocean for climatic changes on a decadal to secular time scale. This scientific challenge is illustrated by estimating the response of the global temperature to changes in trace gas concentration from the pre-industrial epoch to the middle of the next century. A simple energetic formulation is given to estimate the effect on global equilibrium temperature of a fixed instantaneous radiative forcing and of a time-dependent radiative forcing. An atmospheric energy balance model coupled to a box-advection-diffusion ocean model is then used to estimate the past and future global climatic transient response to trace-gas concentration changes. The time-dependent radiative perturbation is estimated from a revised approximate radiative parameterization, and the recent reference set of trace gas scenarios proposed by Wuebbles et al. (1984) are adopted as standard scenarios. Similar computations for the past and future have recently been undertaken by Wigley (1985), but using a purely diffusive ocean and slightly different trace gas scenarios. The skill of the so-called standard experiment is finally assessed by examining the model sensitivity to different parameters such as the equilibrium surface air temperature change for a doubled CO2 concentration [Delta T-ae(2 x CO2)], the heat exchange with the deeper ocean and the trace gas scenarios. For Delta T-ae(2 x CO2) between 1 K and 5 K, the following main results are obtained: (i) for a pre-industrial CO2 concentration of 270 ppmv, the surface air warming between 1850 and 1980 ranges between 0.4 and 1.4 K (if a pre-industrial CO2 concentration of 290 ppmv is chosen, the range is between 0.3 and 1 K); ( ii) by comparison with the instantaneous equilibrium computations, the deeper ocean inertia induces a delay which amounts to between 6 years [for lower Delta T-ae(2 x CO2)] and 23 years [for higher Delta T-ae(2 x CO2)] in 1980; (iii) for the standard future CO2 and other trace gas scenarios of Wuebbles et al., the surface air warming between 1980 and 2050 is calculated to range between 0.9 and 3.4 K, with a delay amounting to between 7 years and 32 years in 2050 when compared to equilibrium computations.
    Lau N.-C., M. J. Nath, 1996: The role of the "atmospheric bridge" in linking tropical Pacific ENSO events to extratropical SST anomalies. J. Climate, 9, 2036- 2057.10.1175/1520-0442(1996)009<2036:TROTBI>2.0.CO; The role of the atmospheric circulation as a “bridge” between sea surface temperature (SST) anomalies in the tropical Pacific and those in the midlatitude northern oceans is assessed. The key processes associated with this atmospheric bridge are described using output from four independent simulations with a general circulation model subjected to month to month SST variations observed in the tropical Pacific during the 1946–1988 period and to climatological SST conditions elsewhere (the “TOGA” runs). In episodes with prominent SST anomalies in the tropical Pacific, extratropical perturbations in the simulated atmospheric temperature, humidity, and wind fields induce changes in the latent and sensible heat fluxes across the air-sea interface of the midlatitude oceans. These anomalous fluxes in turn lead to extratropical SST changes. The relevance of the atmospheric bridge mechanism is evaluated by driving a motionless, 50-m deep oceanic negative mixed layer model at individual grid points with the local surface fluxes generated in the TOGA runs. The negative feedback of the mixed layer temperature anomalies on the imposed flux forcing is taken into account by introducing a linear damping term with a 5-mouth dissipative time scale. This simple system reproduces the basic spatial and temporal characteristics of the observed SST variability in the North Pacific and western North Atlantic. The two-way air-sea feedbacks associated with the atmospheric bridge are investigated by performing four additional 43-year runs of a modified version of the TOGA Experiment. These new “TOGA-ML” runs predict the ocean temperature outside the tropical Pacific by allowing the atmosphere to interact fully with the same mixed layer model mentioned above. The results support the notion that midlatitude ocean-atmosphere interaction can be modeled as a first-order Markov process, in which the red-noise response of mixed layer temperature is driven by white–noise atmospheric forcing in the presence of linear damping. The amplitude of near-surface atmospheric anomalies appearing in the TOGA-ML runs is higher than that in the TOGA runs. This finding implies that, in the TOGA-ML scenario, the midlatitude oceanic responses to atmospheric driving could exert positive feedbacks on the atmosphere, thereby reinforcing the air-sea coupling. The enhanced atmosphere-ocean interactions operating in TOGA-ML prolong the duration of persistent meteorological episodes in that experiment. A comprehensive survey is conducted of the persistence characteristics simulated in TOGA, TOGA- ML, and several other experiments subjected to prescribed SST forcing at various sites. Model scenarios in which observed tropical Pacific SST anomalies act in conjunction with SST perturbations in midlatitudes (either prescribed or predicted) are seen to produce the highest frequency of persistent events.
    Lau N.-C., M. J. Nath, 2003: Atmosphere-ocean variations in the Indo-Pacific sector during ENSO episodes. J. Climate, 16( 1), 3- 20.10.1175/1520-0442(2003)016<0003:AOVITI>2.0.CO; The influences of El Ni&ntilde;o-Southern Oscillation (ENSO) events on air-sea interaction in the Indian-western Pacific (IWP) Oceans have been investigated using a general circulation model. Observed monthly sea surface temperature (SST) variations in the deep tropical eastern/central Pacific (DTEP) have been inserted in the lower boundary of this model through the 1950-99 period. At all maritime grid points outside of DTEP, the model atmosphere has been coupled with an oceanic mixed layer model with variable depth. Altogether 16 independent model runs have been conducted.Composite analysis of selected ENSO episodes illustrates that the prescribed SST anomalies in DTEP affect the surface atmospheric circulation and precipitation patterns in IWP through displacements of the near-equatorial Walker circulation and generation of Rossby wave modes in the subtropics. Such atmospheric responses modulate the surface fluxes as well as the oceanic mixed layer depth, and thereby establish a well-defined SST anomaly pattern in the IWP sector several months after the peak in ENSO forcing in DTEP. In most parts of the IWP region, the net SST tendency induced by atmospheric changes has the same polarity as the local composite SST anomaly, thus indicating that the atmospheric forcing acts to reinforce the underlying SST signal.By analyzing the output from a suite of auxiliary experiments, it is demonstrated that the SST perturbations in IWP (which are primarily generated by ENSO-related atmospheric changes) can, in turn, exert notable influences on the atmospheric conditions over that region. This feedback mechanism also plays an important role in the eastward migration of the subtropical anticyclones over the western Pacific in both hemispheres.
    Lau W. K. M., K.-M. Kim, 2012: The 2010 Pakistan flood and Russian heat wave: Heleconnection of hydrometeorological extremes. Journal of Hydrometeorology, 13, 392- 403.
    Lee J.-Y., B. Wang, Q. Ding, K.-J. Ha, J.-B. Ahn, A. Kumar, B. Stern, and O. Alves, 2011: How predictable is the northern hemisphere summer upper-tropospheric circulation? Climate Dyn., 37, 1189- 1203.10.1007/ retrospective forecast skill of three coupled climate models (NCEP CFS, GFDL CM2.1, and CAWCR POAMA 1.5) and their multi-model ensemble (MME) is evaluated, focusing on the Northern Hemisphere (NH) summer upper-tropospheric circulation along with surface temperature and precipitation for the 25-year period of 1981鈥2005. The seasonal prediction skill for the NH 200-hPa geopotential height basically comes from the coupled models鈥 ability in predicting the first two empirical orthogonal function (EOF) modes of interannual variability, because the models cannot replicate the residual higher modes. The first two leading EOF modes of the summer 200-hPa circulation account for about 84% (35.4%) of the total variability over the NH tropics (extratropics) and offer a hint of realizable potential predictability. The MME is able to predict both spatial and temporal characteristics of the first EOF mode (EOF1) even at a 5-month lead (January initial condition) with a pattern correlation coefficient (PCC) skill of 0.96 and a temporal correlation coefficient (TCC) skill of 0.62. This long-lead predictability of the EOF1 comes mainly from the prolonged impacts of El Nino-Southern Oscillation (ENSO) as the EOF1 tends to occur during the summer after the mature phase of ENSO. The second EOF mode (EOF2), on the other hand, is related to the developing ENSO and also the interdecadal variability of the sea surface temperature over the North Pacific and North Atlantic Ocean. The MME also captures the EOF2 at a 5-month lead with a PCC skill of 0.87 and a TCC skill of 0.67, but these skills are mainly obtained from the zonally symmetric component of the EOF2, not the prominent wavelike structure, the so-called circumglobal teleconnection (CGT) pattern. In both observation and the 1-month lead MME prediction, the first two leading modes are accompanied by significant rainfall and surface air temperature anomalies in the continental regions of the NH extratropics. The MME success in predicting the EOF1 (EOF2) is likely to lead to a better prediction of JJA precipitation anomalies over East Asia and the North Pacific (central and southern Europe and western North America).
    Lee J.-Y., B. Wang, K.-H. Seo, J.-S. Kug, Y.-S. Choi, Y. Kosaka, and K.-J. Ha, 2014: Future change of Northern Hemisphere summer tropical-extratropical teleconnection in CMIP5 models. J. Climate, 27, 3643- 3664.10.1175/ Two dominant global-scale teleconnections in the Northern Hemisphere (NH) extratropics during boreal summer season (June–August) have been identified: the western North Pacific–North America (WPNA) and circumglobal teleconnection (CGT) patterns. These teleconnection patterns are of critical importance for the NH summer seasonal climate prediction. Here, how these teleconnections will change under anthropogenic global warming is investigated using representative concentration pathway 4.5 (RCP4.5) experiments by 20 coupled models that participated in phase 5 of the Coupled Model Intercomparison Project (CMIP5). The six best models are selected based on their performance in simulation of the two teleconnection patterns and climatological means and variances of atmospheric circulation, precipitation, and sea surface temperature. The selected models capture the CGT and its relationship with the Indian summer monsoon (ISM) reasonably well. The models can also capture the WPNA circulation pattern but with striking deficiencies in reproducing its associated rainfall anomalies due to poor simulation of the western North Pacific summer monsoon rainfall. The following changes are anticipated in the latter half of twenty-first century under the RCP4.5 scenario: 1) significant weakening of year-to-year variability of the upper-level circulation due to increased atmospheric stability, although the moderate increase in convective heating over the tropics may act to strengthen the variability; 2) intensification of the WPNA pattern and major spectral peaks, particularly over the eastern Pacific–North America and North Atlantic–Europe sectors, which is attributed to the strengthening of its relationship with the preceding mature phase of El Ni09o–Southern Oscillation (ENSO); and 3) weakening of the CGT due to atmospheric stabilization and decreasing relationship with ISM as well as weakening of the ISM–ENSO relationship.
    Li C. F., R. Y. Lu, and B. W. Dong, 2012: Predictability of the western North Pacific summer climate demonstrated by the coupled models of ENSEMBLES. Climate Dyn., 39, 329- 346.10.1007/ Asian monsoon system, including the western North Pacific (WNP), East Asian, and Indian monsoons, dominates the climate of the Asia-Indian Ocean-Pacific region, and plays a significant role in the
    Li G., S.-P. Xie, and Y. Du, 2015a: Climate model errors over the South Indian Ocean thermocline dome and their effect on the basin mode of interannual variability. J. Climate, 28, 3093- 3098.5a4c384a-25d6-4f1a-8ef4-ccf9ee01a0c2
    Li G., S.-P. Xie, and Y. Du, 2015b: Monsoon-induced biases of climate models over the tropical Indian Ocean. J. Climate, 28, 3058-3072, doi: 10.1175/JCLI-D-14-00740.1.10.1175/ biases of climate models limit the skills of climate prediction and projection. Overlooked are tropical Indian Ocean (IO) errors. Based on the Coupled Model Intercomparison Project Phase 5 (CMIP5) multi-model ensemble, the present study identifies a common error pattern in climate models that resembles the IO Dipole (IOD) mode of interannual variability in nature, with a strong equatorial easterly wind bias during boreal autumn accompanied by physically consistent biases in precipitation, sea surface temperature (SST), and subsurface ocean temperature. The analyses show that such IOD-like biases can be traced back to errors in the South Asian summer monsoon. Too weak a southwest summer monsoon over the Arabian Sea generates a warm SST bias over the western equatorial IO. In boreal autumn, Bjerknes feedback helps amplify the error into an IOD-like bias pattern in wind, precipitation, SST, and subsurface ocean temperature. Such mean state biases result in too strong interannual IOD var...
    Li, J. B., Coauthors , 2013: El Niño modulations over the past seven centuries. Nature Climate Change, 3, 822- 826.10.1038/ how the El Nino/Southern Oscillation (ENSO) will change with global warming is of enormous importance to society(1-4). ENSO exhibits considerable natural variability at interdecadal-centennial timescales(5). Instrumental records are too short to determine whether ENSO has changed(6) and existing reconstructions are often developed without adequate tropical records. Here we present a seven-century-long ENSO reconstruction based on 2,222 tree-ring chronologies from both the tropics and mid-latitudes in both hemispheres. The inclusion of tropical records enables us to achieve unprecedented accuracy, as attested by high correlations with equatorial Pacific corals(7,8) and coherent modulation of global teleconnections that are consistent with an independent Northern Hemisphere temperature reconstruction(9). Our data indicate that ENSO activity in the late twentieth century was anomalously high over the past seven centuries, suggestive of a response to continuing global warming. Climate models disagree on the ENSO response to global warming(3,4), suggesting that many models underestimate the sensitivity to radiative perturbations. Illustrating the radiative effect, our reconstruction reveals a robust ENSO response to large tropical eruptions, with anomalous cooling in the east-central tropical Pacific in the year of eruption, followed by anomalous warming one year after. Our observations provide crucial constraints for improving climate models and their future projections.
    Li S. L., J. Lu, G. Huang, and K. M. Hu, 2008: Tropical Indian Ocean basin warming and East Asian summer monsoon: a multiple AGCM study. J. Climate, 21, 6080- 6088.10.1175/ A basin-scale warming is the leading mode of tropical Indian Ocean sea surface temperature (SST) variability on interannual time scales, and it is also the prominent feature of the interdecadal SST trend in recent decades. The influence of the warming on the East Asian summer monsoon (EASM) is investigated through ensemble experiments of several atmospheric general circulation models (AGCMs). The results from five AGCMs consistently suggest that near the surface, the Indian Ocean warming forces an anticyclonic anomaly over the subtropical western Pacific, intensifying the southwesterly winds to East China; and in the upper troposphere, it forces a Gill-type response with the intensified South Asian high, both favoring the enhancement of the EASM. These processes are argued to contribute to the stronger EASM during the summer following the peak of El Nino than monsoons in other years. These model results also suggest that tropical Indian Ocean warming may not have a causal relationship to the synchronous weakening of EASM on interdecadal time scales.
    Li T. M., B. Wang, 2005: A review on the western North Pacific monsoon: Synoptic-to-interannual variabilities. Terrestrial, Atmospheric and Oceanic Sciences, 16, 285- 314.10.1016/ this paper we review the observed structure and evolution characteristics of the western North Pacific monsoon on various time scales, including its annual cycle, synoptic wave activity, intraseasonal oscillations, and interannual variabilities. On the synoptic (2-10-day) timescale, summertime synoptic waves and equatorial symmetric and anti-symmetric modes are often observed, and they may be responsible for triggering tropical cyclone genesis. On the intraseasonal scale, there are significant spectrum peaks at bi-weekly (10-20-day) and lower-frequency (20-70-day) bands. On the interannual time scale, the monsoon is greatly modulated by and possibly feeds back to the El Nino-Southern Oscillation (ENSO). The paper reviews our current understanding of physical mechanisms that give rise to the synoptic-scale, intraseasonal and interannual variabilities, and multi- scale interactions among these motions. The comparison between the Indian monsoon and the western North Pacific monsoons in terms of their differences in precipitation and circulation patterns, dominant time scales, and global teleconnection is also illustrated. Finally we discuss some remaining issues related to the western North Pacific monsoon variabilities.
    Li X. C., S.-P. Xie, S. T. Gille, and C. Yoo, 2015c: Atlantic-induced pan-tropical climate change over the past three decades. Nature Clim.Change, doi: 10.1038/NCLIMATE 2840.10.1038/
    Li X. Z., W. Zhou, D. L. Chen, C. Y. Li, and J. Song, 2014: Water vapor transport and moisture budget over Eastern China: Remote forcing from the two types of El Niño. J. Climate, 27, 8778- 8792.
    Liang J. Y., S. Yang, Z. Z. Hu, B. H. Huang, A. Kumar, and Z. Q. Zhang, 2009: Predictable patterns of the Asian and Indo-Pacific summer precipitation in the NCEP CFS. Climate Dyn., 32, 989- 1001.10.1007/ predictable patterns of the Asian and Indo-Pacific summer precipitation in the NCEP climate forecast system (CFS) are depicted by applying a maximized signal-to-noise empirical orthogonal function analysis. The CFS captures the two most dominant modes of observed climate patterns. The first most dominant mode is characterized by the climate features of the onset years of El Nino-Southern Oscillation (ENSO), with strong precipitation signals over the tropical eastern Indian and western Pacific oceans, Southeast Asia, and tropical Asian monsoon regions including the Bay of Bengal and the South China Sea. The second most dominant mode is characterized by the climate features of the decay years of ENSO, with weakening signals over the western-central Pacific and strengthening signals over the Indian Ocean. The CFS is capable of predicting the most dominant modes several months in advance. It is also highly skillful in capturing the air鈥搒ea interaction processes associated with the precipitation features, as demonstrated in sea surface temperature and wind patterns.
    Liu L., S.-P. Xie, X.-T. Zheng, T. Li, Y. Du, G. Huang, and W.-D. Yu, 2014: Indian Ocean variability in the CMIP5 multi-model ensemble: The zonal dipole mode. Climate Dyn.,43, 1715-1730, doi: 10.1007/s00382-013-2000-9.10.1007/ performance of 21 Coupled Model Intercomparison Project Phase 5 (CMIP5) models in the simulation of the Indian Ocean Dipole (IOD) mode is evaluated. Compared to CMIP3, CMIP5 models exhibit a similar spread in IOD intensity. A detailed diagnosis was carried out to understand whether CMIP5 models have shown improvement in their representation of the important dynamical and thermodynamical feedbacks in the tropical Indian Ocean. These include the Bjerknes dynamic air-sea feedback, which includes the equatorial zonal wind response to sea surface temperature (SST) anomaly, the thermocline response to equatorial zonal wind forcing, the ocean subsurface temperature response to the thermocline variations, and the thermodynamic air-sea coupling that includes the wind-evaporation-SST and cloud-radiation-SST feedback. Compared to CMIP3, the CMIP5 ensemble produces a more realistic positive wind-evaporation-SST feedback during the IOD developing phase, while the simulation of Bjerknes dynamic feedback is more unrealistic especially with regard to the wind response to SST forcing and the thermocline response to surface wind forcing. The overall CMIP5 performance in the IOD simulation does not show remarkable improvements compared to CMIP3. It is further noted that the El Ni脙卤o-Southern Oscillation (ENSO) and IOD amplitudes are closely related, if a model generates a strong ENSO, it is likely that this model also simulates a strong IOD.
    Liu Z. Y., M. Alexander, 2007: Atmospheric bridge, oceanic tunnel, and global climatic teleconnections. Rev. Geophys., 45,RG2005, doi: 10.1029/2005RG000172.10.1029/[1] We review teleconnections within the atmosphere and ocean, their dynamics and their role in coupled climate variability. We concentrate on teleconnections in the latitudinal direction, notably tropical-extratropical and interhemispheric interactions, and discuss the timescales of several teleconnection processes. The tropical impact on extratropical climate is accomplished mainly through the atmosphere. In particular, tropical Pacific sea surface temperature anomalies impact extratropical climate variability through stationary atmospheric waves and their interactions with midlatitude storm tracks. Changes in the extratropics can also impact the tropical climate through upper ocean subtropical cells at decadal and longer timescales. On the global scale the tropics and subtropics interact through the atmospheric Hadley circulation and the oceanic subtropical cell. The thermohaline circulation can provide an effective oceanic teleconnection for interhemispheric climate interactions.
    Lu R. Y., Z. D. Lin, 2009: Role of subtropical precipitation anomalies in maintaining the summertime meridional teleconnection over the western North Pacific and East Asia. J. Climate, 22, 2058- 2072.10.1175/ meridional teleconnection patterns over the western North Pacific and East Asia (WNP–EA) during summer have a predominant role in affecting East Asian climate on the interannual time scale. A well-known seesaw pattern of tropical–subtropical precipitation is associated with the meridional teleconnection, and the subtropical precipitation anomaly has been previously viewed as a result of anomalous circulations associated with the teleconnection. In this study, however, the authors suggest that subtropical precipitation anomalies, in turn, can significantly affect large-scale circulations and may be crucial for maintenance of the meridional teleconnection. Diagnosis by using observational and reanalysis data indicates that the meridional teleconnection patterns are clearer in summers when the subtropical rainfall anomalies are greater. The simulated results by a linear baroclinic model indicate that a subtropical heat source, which is equivalent to the diagnosed positive subtropical precipitation anomaly, induces zonally elongated zonal wind anomalies that resemble the diagnosed ones in both the upper and lower troposphere over the extratropical WNP–EA. The simulated results also indicate that the horizontal and vertical structures of circulation responses are insensitive to the locations and shapes of imposed subtropical heat anomalies, which implies the important role of basic flow in circulation responses. This study suggests that, for confidential dynamical seasonal forecasting in East Asia, general circulation models should be required to capture the features of interannual subtropical rainfall variability and basic-state flows in WNP–EA.
    Lu R. Y., S. Lu, 2014: Local and remote factors affecting the SST-precipitation relationship over the western North Pacific during summer. J. Climate, 27, 5132- 5147.10.1175/ The western North Pacific (WNP) monsoon variability plays an important role in East Asian climate, and it highlights the importance of understanding atmosphere–ocean interaction determining WNP variability. A key characteristic of atmosphere–ocean interaction is the local relationship between sea surface temperatures and precipitation (SST– P ), which over the WNP exhibits a weak and negative correlation; this indicates that atmospheric variations lead to SST anomalies. This study investigates the underlying physical causes of this relationship, and it suggests that the inverse SST– P relationship over the WNP results from a local anomalous lower-tropospheric anticyclone or cyclone. A strong and negative SST– P correlation corresponds to a strong cyclonic/anticyclonic anomaly, while a weak SST– P relationship is related to a weak circulation anomaly. This study suggests that the remote effects play a crucial role in forming the inverse SST– P relationship over the WNP, while local SSTs tend to result in a positive SST– P correlation and partially offset the remote effects. Furthermore, the negative SST– P relationship over the WNP tends to be associated with rapid transitions of SST anomalies in the equatorial central and eastern Pacific, implying that atmosphere–ocean interaction over the WNP during summer may be affected by and in turn modify the evolution of ENSO.
    Lu R. Y., Y. Li, and B. W. Dong, 2006: External and internal summer atmospheric variability in the western North Pacific and East Asia. J. Meteor. Soc.Japan, 84, 447- 462.10.2151/ interannual variation of summer climate in the western North Pacific and East Asia (WNP/EA) has been investigated in this study using an experiment forced by global observed sea surface temperatures (SSTs). The ensemble integrations enable us to separate externally forced variability from internal variability. It is found that the lower-tropospheric circulation anomaly over the WNP is dominated by the external variability forced by SSTs, while the anomaly of the East Asian jet (EAJ), is dominated by the atmospheric internal variability. The external variability in the WNP/EA sector is mainly reflected by the first leading empirical orthogonal function (EOF) mode of lower-tropospheric zonal wind, and partially by the second mode. The first mode is characterized by a cyclonic/anticyclonic circulation anomaly over the tropical WNP, reflecting changes in the WNP subtropical high. This mode is associated with precipitation and SST anomalies in the tropics. The second mode is characterized by a wave-like pattern of zonal wind in the meridional direction, with zonally-oriented cells over the WNP. This second mode is associated with very weak SST anomalies, and more like a mode of the internal variability. The internal mode is found to be well organized in the WNP/EA sector. The features associated with this mode include the meridional displacement, and intensity variation of EAJ, and precipitation anomaly over the WNP.
    Lu R.-Y., C.-F. Li, S.-H. Yang, and B. W. Dong, 2012: The coupled model predictability of the western North Pacific summer monsoon with different leading times. Atmospheric and Oceanic Science Letters, 5, 219- 224.10.1080/ time length is an important issue for modeling seasonal forecasts. In this study, a comparison of the interannual predictability of the Western North Pacific (WNP) summer monsoon between different leading months was performed by using one-, four-, and sevenmonth lead retrospective forecasts (hindcasts) of four coupled models from Ensembles-Based Predictions of Climate Changes and Their Impacts (ENSEMBLES) for the period of 1960 2005. It is found that the WNP summer anomalies, including lower-tropospheric circulation and precipitation anomalies, can be well predicted for all these leading months. The accuracy of the four-month lead prediction is only slightly weaker than that of the one-month lead prediction, although the skill decreases with the increase of leading months.
    Luo J.-J., S. Masson, S. Behera, and T. Yamagata, 2008: Extended ENSO predictions using a fully coupled ocean-atmosphere model. J. Climate, 21, 84-;link_type=DOI
    Luo J.-J., W. Sasaki, and Y. Masumoto, 2012: Indian Ocean warming modulates Pacific climate change. Proceedings of the National Academy of Sciences of the United States of America, 109, 18 701- 18 706.10.1073/ It has been widely believed that the tropical Pacific trade winds weakened in the last century and would further decrease under a warmer climate in the 21st century. Recent high-quality observations, however, suggest that the tropical Pacific winds have actually strengthened in the past two decades. Precise causes of the recent Pacific climate shift are uncertain. Here we explore how the enhanced tropical Indian Ocean warming in recent decades favors stronger trade winds in the western Pacific via the atmosphere and hence is likely to have contributed to the La Nina-like state (with enhanced east-west Walker circulation) through the Pacific ocean-atmosphere interactions. Further analysis, based on 163 climate model simulations with centennial historical and projected external radiative forcing, suggests that the Indian Ocean warming relative to the Pacific's could play an important role in modulating the Pacific climate changes in the 20th and 21st centuries.
    Masumoto Y., G. Meyers, 1998: Forced Rossby waves in the southern tropical Indian Ocean. J. Geophys. Res., 103( C12), 27 589- 27 602.
    Matsuno T., 1966: Quasi-geostrophic motions in the equatorial area. J. Meteor. Soc.Japan, 44, 25- Quasi-horizontal wave motions in the equatorial area are discussed. A single layer of homogeneous incompressible fluid with free surface is treated. The Coriolis parameter is assumed to be proportional to the latitude. In general, waves of two different types are
    Mei W., S.-P. Xie, M. Zhao, and Y. Q. Wang, 2015: Forced and internal variability of tropical cyclone track density in the western North Pacific. J. Climate, 28, 143-
    Mishra V., B. V. Smoliak, D. P. Lettenmaier, and J. M. Wallace, 2012: A prominent pattern of year-to-year variability in Indian summer monsoon rainfall. Proceedings of the National Academy of Sciences of the United States of America,109, 7213-7217, doi: 10.1073/pnas.1119150109.10.1073/ The dominant patterns of Indian Summer Monsoon Rainfall (ISMR) and their relationships with the sea surface temperature and 850-hPa wind fields are examined using gridded datasets from 1900 on. The two leading empirical orthogonal functions (EOFs) of ISMR over India are used as basis functions for elucidating these relationships. EOF1 is highly correlated with all India rainfall and El Ni&ntilde;o-Southern Oscillation indices. EOF2 involves rainfall anomalies of opposing polarity over the Gangetic Plain and peninsular India. The spatial pattern of the trends in ISMR from 1950 on shows drying over the Gangetic Plain projects onto EOF2, with an expansion coefficient that exhibits a pronounced trend during this period. EOF2 is coupled with the dominant pattern of sea surface temperature variability over the Indian Ocean sector, which involves in-phase fluctuations over the Arabian Sea, the Bay of Bengal, and the South China Sea, and it is correlated with the previous winter's El Ni&ntilde;o-Southern Oscillation indices. The circulation anomalies observed in association with fluctuations in the time-varying indices of EOF1 and EOF2 both involve distortions of the low-level monsoon flow. EOF1 in its positive polarity represents a southward deflection of moist, westerly monsoon flow from the Arabian Sea across India, resulting in a smaller flux of moisture to the Himalayas. EOF2 in its positive polarity represents a weakening of the monsoon trough over northeastern India and the westerly monsoon flow across southern India, reminiscent of the circulation anomalies observed during break periods within the monsoon season.
    Neelin J. D., H. Su, 2005: Moist teleconnection mechanisms for the tropical South American and Atlantic sector. J. Climate, 18, 3928- 3950.10.1175/ have traditionally been studied for the case of dry dynamical response to a given diabatic heat source. Important anomalies often occur within convective zones, for instance, in the observed remote response to El Ni070705o. The reduction of rainfall and teleconnection propagation in deep convective regions poses theoretical challenges because feedbacks involving convective heating and cloud radiative effects come into play. Land surface feedbacks, including variations of land surface temperature, and ocean surface layer temperature response must be taken into account. During El Ni070705o, descent and negative precipitation anomalies often extend across equatorial South America and the Atlantic intertropical convergence zone. Analysis of simulated mechanisms in a case study of the 1997/98 El Ni070705o is used to illustrate the general principals of teleconnections occurring in deep convective zones, contrasting land and ocean regions. Comparison to other simulated events shows similar behavior. Tropospheric temperature and wind anomalies are spread eastward by wave dynamics modified by interaction with the moist convection zones. The traditional picture would have gradual descent balanced by radiative damping, but this scenario misses the most important balances in the moist static energy (MSE) budget. A small 070705zoo070705 of mechanisms is active in producing strong regional descent anomalies and associated drought. Factors common to several mechanisms include the role of convective quasi equilibrium (QE) in linking low-level moisture anomalies to free tropospheric temperature anomalies in a two-way interaction referred to as QE mediation. Convective heating feedbacks change the net static stability to a gross moist stability (GMS) M. The large cloud radiative feedback terms may be manipulated to appear as a modified static stability Meff, under approximations that are quantified for the quasi-equilibrium tropical circulation model used here. The relevant measure of Meff differs between land, where surface energy flux balance applies, and short time scales over ocean. For the time scale of an onsetting El Ni070705o, a mixed layer ocean response is similar to a fixed sea surface temperature (SST) case, with surface fluxes lost into the ocean and Meff substantially reduced over ocean-enhancing descent anomalies. Use of Meff aids analysis of terms that act as the initiators of descent anomalies. Apparently modest terms in the MSE budget can be acted on by the GMS multiplier effect, which yields substantial precipitation anomalies due to the large ratio of the moisture convergence to the MSE divergence. Advection terms enter in several mechanisms, with the leading effects here due to advection by mean winds in both MSE and momentum balances. A Kelvinoid solution is presented as a prototype for how easterly flow enhances moist wave decay mechanisms, permitting relatively small damping terms by surface drag and radiative damping to produce the substantial eastward temperature gradients seen in observations and simulations and contributing to precipitation anomalies. The leading mechanism for drought in eastern equatorial South America is the upped-ante mechanism in which QE mediation of teleconnected tropospheric temperature anomalies tends to produce moisture gradients between the convection zone, where low-level moisture increases toward QE, and the neighboring nonconvective region. Over the Atlantic ITCZ, the upped-ante mechanism is a substantial contributor, but on short time scales several mechanisms referred to jointly as troposphere/SST disequilibrium mechanisms are important. While SST is adjusting during passive SST (coupled ocean mixed layer) experiments, or for fixed SST, heat flux to the ocean is lost to the atmosphere, and these mechanisms can induce descent and precipitation anomalies, although they disappear when SST equilibrates. In simulations here, cloud radiative feedbacks, surface heat fluxes induced by teleconnected wind anomalies, and surface fluxes induced by QE-mediated temperature anomalies are significant disequilibrium contributors. At time scales of several months or longer, remaining Atlantic ITCZ rainfall reductions are maintained by the upped-ante mechanism.
    Nigam S., H.-S. Shen, 1993: Structure of Oceanic and Atmospheric Low-Frequency Variability over the Tropical Pacific and Indian Oceans. Part I: COADS observations. J. Climate, 6, 657- 676.
    Nitta T., 1986: Long-term variations of cloud amount in the western Pacific region. J. Meteor. Soc.Japan, 64, 373- 390.
    Nitta T., 1987: Convective activities in the tropical western Pacific and their impact on the Northern Hemisphere summer circulation. J. Meteor. Soc.Japan, 65, 373- 390.10.1175/1520-0469(1987)044<1554:TAOPVT>2.0.CO;, à l'aide de la couverture nuageuse vue par satellite, de la TSM (SST) et du géopotentiel, toutes données sur 7 ans (1978-84), des variations interannuelle et intrasaisonnière de l'activité convective en été, dans le Pacifique tropical ouest, ainsi que de l'impact sur la circulation dans l'hémisphère nord. Résultats principaux: lorsque la TSM est plus chaude de 1,0°C que la normale, les régions de convection active (typhons, dépressions tropicales) se déplacent vers le NE à partir d'une position normale près des Philippines jusqu'à 20 N, la couverture nuageuse dans les zones tempérée et équatoriale est fortement atténuée; une anomalie de haute p prédomine dans la zone tempérée (de la Chine est jusqu'au Pacifique nord); l'activité convective est très modulée par la variation intrasaisonnière; il existe des trains d'ondes de hauteur géopotentielle qui émanent de la source de chaleur qui s'étend des Philippines à l'Amérique du Nord; ils sont générés lorsque l'activité convective dans la mer des Philippines devient intense; en conclusion les ondes de Rossby sont générées par la source de chaleur associée à la variation intrasaisonnière; des anomalies de p en Asie de l'Est peuvent être considérées comme une conséquence de la génération de ces ondes
    Ogata T., S.-P. Xie, A. Wittenberg, and D.-Z. Sun, 2013: Interdecadal amplitude modulation of El Niño-Southern oscillation and its impact on tropical Pacific decadal variability. J. Climate, 26, 7280- 7297.
    Ohba M., H. Ueda, 2006: A role of zonal gradient of SST between the Indian Ocean and the western Pacific in localized convection around the Philippines. Scientific Online Lettrs on the Atmosphere,2, 176-179, doi: 10.2151/sola.2006-045.10.2151/ fluctuations of the convective activity around the Philippines are highly correlated with the east-west gradient of SST between the North Indian Ocean (NIO) and the western North Pacific (WNP). We conducted a set of experiments by use of an atmospheric general circulation model (AGCM) to assess the relative importance of the remote (NIO) versus in situ (WNP) SST anomalies in determining the WNP monsoon rainfall as ocean-to-atmosphere feedback. The solutions indicate that both in situ and remote SST anomalies regulate precipitation around the Philippines in the early summer. This result implies that the WNP monsoon rainfall is sensitive to the spatial distribution of the NIO SST anomalies as well as the in situ anomalies. These physical interpretations suggest further increase of the predictability in the WNP monsoon.
    Otomi Y., Y. Tachibana, and T. Nakamura, 2013: A possible cause of the AO polarity reversal from winter to summer in 2010 and its relation to hemispheric extreme summer weather. Climate Dyn., 40, 1939- 1947.10.1007/ 2010, the Northern Hemisphere, in particular Russia and Japan, experienced an abnormally hot summer characterized by record-breaking warm temperatures and associated with a strongly positive Arctic Oscillation (AO), that is, low pressure in the Arctic and high pressure in the midlatitudes. In contrast, the AO index the previous winter and spring (2009/2010) was record-breaking negative. The AO polarity reversal that began in summer 2010 can explain the abnormally hot summer. The winter sea surface temperatures (SST) in the North Atlantic Ocean showed a tripolar anomaly pattern—warm SST anomalies over the tropics and high latitudes and cold SST anomalies over the midlatitudes—under the influence of the negative AO. The warm SST anomalies continued into summer 2010 because of the large oceanic heat capacity. A model simulation strongly suggested that the AO-related summertime North Atlantic oceanic warm temperature anomalies remotely caused blocking highs to form over Europe, which amplified the positive summertime AO. Thus, a possible cause of the AO polarity reversal might be the “memory” of the negative winter AO in the North Atlantic Ocean, suggesting an interseasonal linkage of the AO in which the oceanic memory of a wintertime negative AO induces a positive AO in the following summer. Understanding of this interseasonal linkage may aid in the long-term prediction of such abnormal summer events.
    Pai D. S., O. P. Sreejith, 2011: Global and Regional circulation anomalies: A report. A. Tyagi et al.,Eds., IMD Met. Monograph No. Synoptic Meteorology No.10/2011, IMD, 63- 78.
    Park H.-S., J. C. H. Chiang, B. R. Lintner, and G. J. Zhang, 2010: The delayed effect of major El Niño events on Indian monsoon rainfall. J. Climate, 23, 932- 946.10.1175/ studies have shown that boreal summer Indian monsoon rainfall is, on average, significantly above normal after major El Ni09o events. In this study, the underlying causes of this rainfall response are examined using both observational analysis and atmospheric general circulation model (AGCM) simulations. Moist static energy budgets for two strong El Ni09o events (1982/83 and 1997/98), es...
    Perigaud C., P. Delecluse, 1993: Interannual Sea level variations in the tropical Indian Ocean from geosat and shallow water simulations. J. Phys. Oceanogr., 23, 1916- 1934.10.1175/1520-0485(1993)0232.0.CO; Sea Level variations of the Indian Ocean north of 20°S are analyzed from Geosat satellite altimeter data over April 1985–September 1989. These variations are compared and interpreted with numerical simulations derived from a reduced gravity model forced by FSU observed winds over the same period. After decomposition into complex empirical orthogonal function the low-frequency anomalies are described by the first two modes for observations as well as for simulations. The sums of the two modes contain 34% and 40% of the observed and simulated variances respectively. Averaged over the basin, the observed and simulated sea level changes are correlated by 0.92 over 1985–1988. The strongest change happens during the El Ni09o 1986–1987, between winter 1986 and summer 1987 the basin-averaged sea level rises by 651 cm. These low-frequency variations can partly be explained by changes in the Sverdrup circulation. The southern tropical Indian Ocean between 10° and 20°S is the domain where those changes are strongest: the averaged sea level rises by 654.5 cm between winter 1986 and winter 1987. There, the signal propagates southwestward across the basin at a speed similar to free Rossby waves. Sensitivity of observed anomalies is examined over 1987–1988, with different orbit ephemeris, tropospheric corrections, and error reduction processes. The uncertainty of the basin-averaged sea level estimates is mostly due to the way the orbit error is reduced and reaches 651 cm. Nonetheless, spatial correlation is good between the various observations and better than between observations and simulations. Sensitivity of simulated anomalies to the wind uncertainty, examined with FSU and ECMWF forcings over 1985–1988, shows that the variance of the simulations driven by ECMWF is 52% smaller, as FSU winds are stronger than ECMWF. Results show that the wind strength also affects the dynamic response of the ocean: anomalies propagate westward across the basin more than twice as fast with FSU than with ECMWF. It is found that the discrepancy is larger between ECMWF and FSU simulations than between observations and FSU simulations.
    Rong X. Y., R. H. Zhang, and T. Li, 2010: Impacts of Atlantic sea surface temperature anomalies on Indo-East Asian summer monsoon-ENSO relationship. Chinese Science Bulletin, 55, 2458- 2468.10.1007/ this study, the effect of the tropical North Atlantic (TNA) sea surface temperature (SST) variation in inducing the circulation anomaly in the Indo-East Asian monsoon (IEAM) region is investigated through the observational analysis and numerical modeling. The observational analysis shows that the TNA summer SST is positively correlated with the preceding winter Ni o3 SST and is simultaneously correlated with the circulation in the IEAM region. The simultaneous circulation pattern resembles that of the ENSO-decaying summer. The positive correlation between the TNA SST and the Ni o3 region SST is primarily ascribed to the surface latent heat flux and short wave radiation anomalies induced by the ENSO teleconnection. Coupled general circulation model experiments show that, while including the air-sea coupling in the Atlantic, the model can reproduce the main features of the IEAM circulation, such as an anomalous anticyclone over the western North Pacific (WNP) and southerly anomalies over southeast China. While the climatological Atlantic SST is prescribed, the circulation over the WNP displays a significantly different pattern, with an eastward migration of the WNP anticyclone and the associated northerly anomalies over southeast China. It is argued that anticyclonic shear and Ekman divergence associated with the atmospheric Kelvin wave response to the TNA warm SSTA forcing is the primary mechanism for the generation of the anomalous anticyclone in WNP. The results presented in this study provide a teleconnection pattern between TNA and short-term climate variability in IEAM region.
    Saha K., 1970: Zonal anomaly of sea surface temperature in equatorial Indian Ocean and its possible effect upon monsoon circulation. Tellus,22, doi: 10.1111/j.2153-3490.1970.tb00506, 403-409. x.10.1111/ The paper calls attention to the existence of a well-defined zonal anomaly of sea surface temperature between the equatorial west and east Indian ocean. The effect of this anomaly on ocean-atmosphere exchange and low-level air circulation in the equatorial Indian ocean as well as the Arabian Sea are discussed. It is shown that phenomena like the equatorial westerlies, the double intertropical convergence zone, and the Somali Jet receive plausible explanation on the basis of the observed zonal anomaly of ocean temperature. The effect of upwelling and its eastward advance in the Arabian Sea during the southwest monsoon are discussed in detail and it is suggested that this effect through air-sea interaction may change the low-level air circulation over the Arabian sea in a manner which may affect the distribution of rainfall along the west coast of India as well as inland during August and also explain frequent occurrence of feeble low pressure troughs in the southeast Arabian Sea during this period. Vertical circulation cells attributable to the observed anomalies of ocean temperature and their possible effect upon monsoon circulation and rain are discussed.
    Saji N. H., B. N. Goswami, P. N. Vinayachand ran, and T. Yamagata, 1999: A dipole mode in the tropical Indian Ocean. Nature, 401, 360- 363.10.1038/ the tropical Pacific and Atlantic oceans, internal modes of variability that lead to climatic oscillations have been recognized, but in the Indian Ocean region a similar ocean-atmosphere interaction causing interannual climate variability has not yet been found. Here we report an analysis of observational data over the past 40 years, showing a dipole mode in the Indian Ocean: a pattern of internal variability with anomalously low sea surface temperatures off Sumatra and high sea surface temperatures in the western Indian Ocean, with accompanying wind and precipitation anomalies. The spatio-temporal links between sea surface temperatures and winds reveal a strong coupling through the precipitation field and ocean dynamics. This air-sea interaction process is unique and inherent in the Indian Ocean, and is shown to be independent of the El Nino/Southern Oscillation. The discovery of this dipole mode that accounts for about 12% of the sea surface temperature variability in the Indian Ocean--and, in its active years, also causes severe rainfall in eastern Africa and droughts in Indonesia--brightens the prospects for a long-term forecast of rainfall anomalies in the affected countries.
    Saji N. H., S.-P. Xie, and T. Yamagata, 2006: Tropical Indian Ocean variability in the IPCC twentieth-century climate simulations. J. Climate, 19, 4397- 4417.10.1175/ twentieth-century simulations using by 17 coupled ocean17atmosphere general circulation models (CGCMs) submitted to the Intergovernmental Panel on Climate Change17s Fourth Assessment Report (IPCC AR4) are evaluated for their skill in reproducing the observed modes of Indian Ocean (IO) climate variability. Most models successfully capture the IO17s delayed, basinwide warming response a few months after El Ni17o17Southern Oscillation (ENSO) peaks in the Pacific. ENSO17s oceanic teleconnection into the IO, by coastal waves through the Indonesian archipelago, is poorly simulated in these models, with significant shifts in the turning latitude of radiating Rossby waves. In observations, ENSO forces, by the atmospheric bridge mechanism, strong ocean Rossby waves that induce anomalies of SST, atmospheric convection, and tropical cyclones in a thermocline dome over the southwestern tropical IO. While the southwestern IO thermocline dome is simulated in nearly all of the models, this ocean Rossby wave response to ENSO is present only in a few of the models examined, suggesting difficulties in simulating ENSO17s teleconnection in surface wind. A majority of the models display an equatorial zonal mode of the Bjerknes feedback with spatial structures and seasonality similar to the Indian Ocean dipole (IOD) in observations. This success appears to be due to their skills in simulating the mean state of the equatorial IO. Corroborating the role of the Bjerknes feedback in the IOD, the thermocline depth, SST, precipitation, and zonal wind are mutually positively correlated in these models, as in observations. The IOD17ENSO correlation during boreal fall ranges from -0.43 to 0.74 in the different models, suggesting that ENSO is one, but not the only, trigger for the IOD.
    Schott F. A., S.-P. Xie, and J. P. McCreary Jr, 2009: Indian Ocean circulation and climate variability. Rev. Geophys, 47,RG1002, doi: 10.1029/2007RG000245.10.1029/ In recent years, the Indian Ocean (IO) has been discovered to have a much larger impact on climate variability than previously thought. This paper reviews climate phenomena and processes in which the IO is, or appears to be, actively involved. We begin with an update of the IO mean circulation and monsoon system. It is followed by reviews of ocean/atmosphere phenomenon at intraseasonal, interannual, and longer time scales. Much of our review addresses the two important types of interannual variability in the IO, El Ni&ntilde;o-Southern Oscillation (ENSO) and the recently identified Indian Ocean Dipole (IOD). IOD events are often triggered by ENSO but can also occur independently, subject to eastern tropical preconditioning. Over the past decades, IO sea surface temperatures and heat content have been increasing, and model studies suggest significant roles of decadal trends in both the Walker circulation and the Southern Annular Mode. Prediction of IO climate variability is still at the experimental stage, with varied success. Essential requirements for better predictions are improved models and enhanced observations.
    Shen S. H., K.-M. Lau, 1995: Biennial oscillation associated with the East Asian summer monsoon and tropical sea surface temperatures. J. Meteor. Soc.Japan, 73, 105- this paper, the interannual variability of the East Asian summer monsoon (EASM) rainfall and the tropical sea surface temperature (SST) have been studied. It is found that the EASM rainfall possesses a strong biennial signal, which is particularly pronounced over the southeast China. For the SST, the biennial oscillation is the second most significant quasi-periodic signal over the entire tropical Indian and Pacific Oceans. Results indicate that the biennial variations in the SST and EASM rainfall are closely linked. The SST pattern which is best correlated with EASM rainfall appears in the form of a double see-saw with quasi-stationary centers of action over the Indian Ocean, the Asian monsoon region and the eastern Pacific. The most pronounced SST signals are found in the equatorial eastern Pacific and Indian Ocean about two seasons preceding and following the EASM rainfall. Evidence is presented suggesting that the biennial variability of the EASM rainfall is phase-locked to a global scale biennial oscillation involving the interplay of the Asian monsoon, the Hadley and Walker circulations, and basin wide fluctuations in SST. In particular, the eastward propagation of zonal wind anomalies from the Indian Ocean to the western Pacific, which regulates the moisture fluxes from the western Pacific to the East Asian region, appears to be a key component of the biennial fluctuation associated with EASM rainfall. Results suggest that the relationship between the Asian monsoon and tropical SST is more robust in the biennial than the ENSO time scale, hence raising the possibility that the biennial oscillation may be more fundamentally related to monsoon-ocean-atmosphere interaction than ENSO itself.
    Simmons A. J., J. M. Wallace, and G. W. Branstator, 1983: Barotropic wave propagation and instability, and atmospheric teleconnection patterns. J. Atmos. Sci., 40, 1363-
    Smith T. M., R. W. Reynolds, T. C. Peterson, and J. Lawrimore, 2008: Improvements to NOAA's Historical Merged Land-Ocean Surface Temperature Analysis (1880-2006). J. Climate, 21, 2283- 2296.
    Stuecker M. F., A. Timmermann, F.-F. Jin, S. McGregor, and H.-L. Ren, 2013: A combination mode of the annual cycle and the El Niño/Southern oscillation. Nature Geoscience, 6, 540-
    Stuecker M. F., F.-F. Jin, A. Timmermann, and S. McGregor, 2015: Combination mode dynamics of the anomalous Northwest Pacific anticyclone. J. Climate, 28, 1093- 1111.10.1175/ Nonlinear interactions between ENSO and the western Pacific warm pool annual cycle generate an atmospheric combination mode (C-mode) of wind variability. The authors demonstrate that C-mode dynamics are responsible for the development of an anomalous low-level northwest Pacific anticyclone (NWP-AC) during El Ni09o events. The NWP-AC is embedded in a large-scale meridionally antisymmetric Indo-Pacific atmospheric circulation response and has been shown to exhibit large impacts on precipitation in Asia. In contrast to previous studies, the authors find the role of air–sea coupling in the Indian Ocean and northwestern Pacific only of secondary importance for the NWP-AC genesis. Moreover, the NWP-AC is clearly marked in the frequency domain with near-annual combination tones, which have been overlooked in previous Indo-Pacific climate studies. Furthermore, the authors hypothesize a positive feedback loop involving the anomalous low-level NWP-AC through El Ni09o and C-mode interactions: the development of the NWP-AC as a result of the C-mode acts to rapidly terminate El Ni09o events. The subsequent phase shift from retreating El Ni09o conditions toward a developing La Ni09a phase terminates the low-level cyclonic circulation response in the central Pacific and thus indirectly enhances the NWP-AC and allows it to persist until boreal summer. Anomalous local circulation features in the Indo-Pacific (e.g., the NWP-AC) can be considered a superposition of the quasi-symmetric linear ENSO response and the meridionally antisymmetric annual cycle modulated ENSO response (C-mode). The authors emphasize that it is not adequate to assess ENSO impacts by considering only interannual time scales. C-mode dynamics are an essential (extended) part of ENSO and result in a wide range of deterministic high-frequency variability.
    Sun X. G., R. J. Greatbatch, W. Park, and M. Latif, 2010: Two major modes of variability of the East Asian summer monsoon. Quart. J. Roy. Meteor. Soc., 136, 829- 841.10.1002/ study the two primary modes of variability associated with the East Asian summer monsoon, as identified using a multivariate Empirical Orthogonal Function (EOF) analysis. The second mode is shown to be related to changes in intensity of the South Asian High at 100 hPa while, consistent with previous work, the first mode is associated with an index for the shear vorticity of the 850 hPa zonal wind over the monsoon region. We show that a linear, dry dynamical model, when driven by the diabatic heating anomalies associated with each mode, can reproduce many of the anomalous circulation features, especially for the first EOF and in the lower troposphere. The model results indicate the importance of diabatic heating anomalies over the tropical Indian Ocean in the dynamics of both modes, especially EOF-1, and illustrate the role of local diabatic feedback for intensifying the circulation anomalies; in particular, the subtropical anticyclonic anomalies that are found in the positive phase of both modes, and the circulation anomaly associated with the Meiyu/Changma/Baiu rain band. A running cross-correlation analysis shows that the second EOF is consistently linked to both the decaying and the onset phase of El Nino/Southern Oscillation (ENSO) events throughout the study period (1958鈥2001). We attribute the connection in the onset phase to zonal wind anomalies along the Equator in the west Pacific associated with this mode. On the other hand, a link between the first EOF and ENSO is found only in the post-1979 period. We note also the role of sea-surface temperature anomalies in the tropical Indian Ocean in the dynamics of EOF-1, and a link to the variability of the Indian summer monsoon in the case of EOF-2. Copyright 漏 2010 Royal Meteorological Society
    Terao T., T. Kubota, 2005: East-west SST contrast over the tropical oceans and the post El Niño western North Pacific summer monsoon. Geophys. Res. Lett., 32, L15706.10.1029/ The circulation and SST anomalies during the post El Ni&ntilde;o Asian summer monsoon season were examined through data analysis and linear equatorial 尾 plane model calculations. Over the Philippine Sea, a negative precipitation anomaly and low-level anti-cyclonic anomaly were found. Over the western equatorial Pacific, a low-level easterly anomaly prevailed. An east-west SST anomaly contrast dominated over the tropical Indian and Pacific Oceans, with positive anomalies over the Indian and western Pacific Oceans and negative anomalies over the central to eastern Pacific. The 尾 plane model demonstrated that the anti-cyclonic anomaly over the Philippine Sea was a Rossby response to the negative precipitation anomaly found in this region. The easterly anomaly along the equator was part of a Kelvin response to the SST anomaly contrast. On the northern side of this anomalous easterly, a negative vorticity anomaly developed. This could induce the moist Rossby wave over the Philippine Sea.
    Tokinaga H., S.-P. Xie, A. Timmermann, S. McGregor, T. Ogata, H. Kubota, and Y. M. Okumura, 2012: Regional patterns of tropical Indo-Pacific climate change: Evidence of the Walker Circulation weakening. J. Climate, 25, 1689- 1710.10.1175/ Regional patterns of tropical Indo-Pacific climate change are investigated over the last six decades based on a synthesis of in situ observations and ocean model simulations, with a focus on physical consistency among sea surface temperature (SST), cloud, sea level pressure (SLP), surface wind, and subsurface ocean temperature. A newly developed bias-corrected surface wind dataset displays westerly trends over the western tropical Pacific and easterly trends over the tropical Indian Ocean, indicative of a slowdown of the Walker circulation. This pattern of wind change is consistent with that of observed SLP change showing positive trends over the Maritime Continent and negative trends over the central equatorial Pacific. Suppressed moisture convergence over the Maritime Continent is largely due to surface wind changes, contributing to observed decreases in marine cloudiness and land precipitation there. Furthermore, observed ocean mixed layer temperatures indicate a reduction in zonal contrast in the tropical Indo-Pacific characterized by larger warming in the tropical eastern Pacific and western Indian Ocean than in the tropical western Pacific and eastern Indian Ocean. Similar changes are successfully simulated by an ocean general circulation model forced with the bias-corrected wind stress. Whereas results from major SST reconstructions show no significant change in zonal gradient in the tropical Indo-Pacific, both bucket-sampled SSTs and nighttime marine air temperatures (NMAT) show a weakening of the zonal gradient consistent with the subsurface temperature changes. All these findings from independent observations provide robust evidence for ocean鈥揳tmosphere coupling associated with the reduction in the Walker circulation over the last six decades.
    Trenberth K. E., G. W. Branstator, D. Karoly, A. Kumar, N.-C. Lau, and C. Ropelewski, 1998: Progress during TOGA in understanding and modeling global teleconnections associated with tropical sea surface temperatures. J. Geophys. Res., 103, 14 291- 14 324.10.1029/ primary focus of this review is tropical-extratropical interactions and especially the issues involved in determining the response of the extratropical atmosphere to tropical forcing associated with sea surface temperature (SST) anomalies. The review encompasses observations, empirical studies, theory and modeling of the extratropical teleconnections with a focus on developments over the Tropical Oceans-Global Atmosphere (TOGA) decade and the current state of understanding. In the tropical atmosphere, anomalous SSTs force anomalies in convection and large-scale overturning with subsidence in the descending branch of the local Hadley circulation. The resulting strong upper tropospheric divergence in the tropics and convergence in the subtropics act as a Rossby wave source. The climatological stationary planetary waves and associated jet streams, especially in the northern hemisphere, can make the total Rossby wave sources somewhat insensitive to the position of the tropical heating that induces them and thus can create preferred teleconnection response patterns, such as the Pacific-North American (PNA) pattern. However, a number of factors influence the dispersion and propagation of Rossby waves through the atmosphere, including zonal asymmetries in the climatological state, transients, and baroclinic and nonlinear effects. Internal midlatitude sources can amplify perturbations. Observations, modeling, and theory have clearly shown how storm tracks change in response to changes in quasi-stationary waves and how these changes generally feedback to maintain or strengthen the dominant perturbations through vorticity and momentum transports. The response of the extratropical atmosphere naturally induces changes in the underlying surface, so that there are changes in extratropical SSTs and changes in land surface hydrology and moisture availability that can feedback and influence the total response. Land surface processes are believed to be especially important in spring and summer. Anomalous SSTs and tropical forcing have tended to be strongest in the northern winter, and teleconnections in the southern hemisphere are weaker and more variable and thus more inclined to be masked by natural variability. Occasional strong forcing in seasons other than winter can produce strong and identifiable signals in the northern hemisphere and, because the noise of natural variability is less, the signal-to-noise ratio can be large. The relative importance of tropical versus extratropical SST forcings has been established through numerical experiments with atmospheric general circulation models (AGCMs). Predictability of anomalous circulation and associated surface temperature and precipitation in the extratropics is somewhat limited by the difficulty of finding a modest signal embedded in the high level of noise from natural variability in the extratropics, and the complexity and variety of the possible feedbacks. Accordingly, ensembles of AGCM runs and time averaging are needed to identify signals and make predictions. Strong anomalous tropical forcing provides opportunities for skillful forecasts, and the accuracy and usefulness of forecasts is expected to improve as the ability to forecast the anomalous SSTs improves, as models improve, and as the information available from the mean and the spread of ensemble forecasts is better utilized.
    Tsuyuki T., K. Kurihara, 1989: Impact of convective activity in the west-ern tropical Pacific on the East Asian summer circulation. J. Meteor. Soc.Japan, 67, 231- 247.10.1175/1520-0469(1989)046<1042:NMRWOI>2.0.CO; of convective activity in the western tropical Pacific on the East Asian summer circulation TSUYUKI T. J. Meteor. Soc. Japan 67, 231-247, 1989
    Ueda H., J. Matsumoto, 2000: A possible triggering process of east-west asymmetric anomalies over the Indian Ocean in relation to 1997/98 El Niño. J. Meteor. Soc.Japan, 78, 803- Anomalous east—west asymmetric anomalies were seen in sea surface temperature (SST), and convective activity over the equatorial Indian Ocean during October—December 1997. Using N CEP/NCAR reanalysis and sea surface height data obtained
    Vecchi, G. A., Coauthors , 2014: On the seasonal forecasting of regional tropical cyclone activity. J. Climate, 27, 7994- 8016.10.1175/ Tropical cyclones (TCs) are a hazard to life and property and a prominent element of the global climate system; therefore, understanding and predicting TC location, intensity, and frequency is of both societal and scientific significance. Methodologies exist to predict basinwide, seasonally aggregated TC activity months, seasons, and even years in advance. It is shown that a newly developed high-resolution global climate model can produce skillful forecasts of seasonal TC activity on spatial scales finer than basinwide, from months and seasons in advance of the TC season. The climate model used here is targeted at predicting regional climate and the statistics of weather extremes on seasonal to decadal time scales, and comprises high-resolution (50 km × 50 km) atmosphere and land components as well as more moderate-resolution (~100 km) sea ice and ocean components. The simulation of TC climatology and interannual variations in this climate model is substantially improved by correcting systematic ocean biases through “flux adjustment.” A suite of 12-month duration retrospective forecasts is performed over the 1981–2012 period, after initializing the climate model to observationally constrained conditions at the start of each forecast period, using both the standard and flux-adjusted versions of the model. The standard and flux-adjusted forecasts exhibit equivalent skill at predicting Northern Hemisphere TC season sea surface temperature, but the flux-adjusted model exhibits substantially improved basinwide and regional TC activity forecasts, highlighting the role of systematic biases in limiting the quality of TC forecasts. These results suggest that dynamical forecasts of seasonally aggregated regional TC activity months in advance are feasible.
    Wakabayashi S., R. Kawamura, 2004: Extraction of major teleconnection patterns possibly associated with the anomalous summer climate in Japan. J. Meteor. Soc.Japan, 82, 1577- 1588.
    Wang B., R. G. Wu, and X. H. Fu, 2000: Pacific-East Asian teleconnection: How does ENSO affect East Asian climate? J. Climate, 13, 1517-
    Wang B., R. G. Wu, and T. Li, 2003: Atmosphere-warm ocean interaction and its impacts on Asian-Australian monsoon variation. J. Climate, 16, 1195-
    Wang B., Q. H. Ding, X. H. Fu, I.-S. Kang, K. Jin, J. Shukla, and F. Doblas-Reyes, 2005: Fundamental challenge in simulation and prediction of summer monsoon rainfall. Geophys. Res. Lett., 32, L15711.10.1029/[1] The scientific basis for two-tier climate prediction lies in the predictability determined by the ocean and land surface conditions. Here we show that the state-of-the-art atmospheric general circulation models (AGCMs), when forced by observed sea surface temperature (SST), are unable to simulate properly Asian-Pacific summer monsoon rainfall. All models yield positive SST-rainfall correlations in the summer monsoon that are at odds with observations. The observed lag correlations between SST and rainfall suggest that treating monsoon as a slave possibly results in the models' failure. We demonstrate that an AGCM, coupled with an ocean model, simulates realistic SST-rainfall relationships; however, the same AGCM fails when forced by the same SSTs that are generated in its coupled run, suggesting that the coupled ocean-atmosphere processes are crucial in the monsoon regions where atmospheric feedback on SST is critical. The present finding calls for reshaping of current strategies for monsoon seasonal prediction. The notion that climate can be modeled and predicted by prescribing the lower boundary conditions is inadequate for validating models and predicting summer monsoon rainfall.
    Wang B., J. Yang, T. J. Zhou, and B. Wang, 2008: Interdecadal changes in the major modes of Asian-Australian monsoon Variability: Strengthening relationship with ENSO since the Late 1970s. J. Climate, 21, 1771- 1789.10.1175/ present paper develops an integral view of the year-to-year variability across the entire Asian17Australian monsoon (A17AM) system, which covers one-third of the global tropics between 4017 and 16017E. Using season-reliant empirical orthogonal function (S-EOF) analysis, the authors identified two major modes of variability for the period 1956172004. The first exhibits a prominent biennial tendency and concurs with the turnabout of El Ni17o17Southern Oscillation (ENSO), providing a new perspective of the seasonally evolving spatiotemporal structure for tropospheric biennial oscillation. The second mode leads ENSO by one year. The remote El Ni17o forcing, the monsoon17warm pool ocean interaction, and the influence of the annual cycle are three fundamental factors for understanding the behavior of the first mode. The monsoon17ocean interaction is characterized by a positive feedback between the off-equatorial convectively coupled Rossby waves and the underlying sea surface temperature (SST) 17dipole17 anomalies. Since the late 1970s the overall coupling between the A17AM system and ENSO has become strengthened. The relationships between ENSO and the western North Pacific, East Asian, and Indonesian monsoons have all become enhanced during ENSO17s developing, mature, and decaying phases, overriding the weakening of the Indian monsoon17ENSO anticorrelation during the developing phase. Prior to the late 1970s (19561779), the first mode shows a strong biennial tendency, and the second mode does not lead ENSO. After 1980, the first mode shows a weakening biennial tendency, and the second mode provides a strong precursory signal for ENSO. These interdecadal changes are attributed to increased magnitude and periodicity of ENSO and the strengthened monsoon17ocean interaction.
    Wang B., Coauthors , 2009: Advance and prospectus of seasonal prediction: Assessment of the APCC/CliPAS 14-model ensemble retrospective seasonal prediction (1980-2004). Climate Dyn., 33, 93-
    Wang B., B. Q. Xiang, and J.-Y. Lee, 2013: Subtropical high predictability establishes a promising way for monsoon and tropical storm predictions. Proceedings of the National Academy of Sciences of the United States of America, 110, 2718- 2722.10.1073/ rainfall and tropical storms (TSs) impose great impacts on society, yet their seasonal predictions are far from successful. The western Pacific Subtropical High (WPSH) is a prime circulation system affecting East Asian summer monsoon (EASM) and western North Pacific TS activities, but the sources of its variability and predictability have not been established. Here we show that the WPSH variation faithfully represents fluctuations of EASM strength (r = -0.92), the total TS days over the subtropical western North Pacific (r = -0.81), and the total number of TSs impacting East Asian coasts (r = -0.76) during 1979-2009. Our numerical experiment results establish that the WPSH variation is primarily controlled by central Pacific cooling/warming and a positive atmosphere-ocean feedback between the WPSH and the Indo-Pacific warm pool oceans. With a physically based empirical model and the state-of-the-art dynamical models, we demonstrate that the WPSH is highly predictable; this predictability creates a promising way for prediction of monsoon and TS. The predictions using the WPSH predictability not only yields substantially improved skills in prediction of the EASM rainfall, but also enables skillful prediction of the TS activities that the current dynamical models fail. Our findings reveal that positive WPSH-ocean interaction can provide a source of climate predictability and highlight the importance of subtropical dynamics in understanding monsoon and TS predictability.
    Wang C. Z., R. H. Weisberg, and J. I. Virmani, 1999: Western Pacific interannual variability associated with the El Niño-Southern oscillation. J. Geophys. Res., 104, 5131- 5149.10.1029/ of sea surface temperature (SST), sea level pressure (SLP), surface wind, and outgoing longwave radiation (OLR) show that the El Nino-Southern Oscillation (ENSO) displays western Pacific anomaly patterns in addition to eastern Pacific anomaly patterns. During the warm phase of ENSO, warm;SST and low SLP anomalies in the equatorial eastern Pacific and low OLR anomalies in the equatorial central Pacific are accompanied by cold SST and high SLP anomalies in the off-equatorial western Pacific and high OLR anomalies in the off-equatorial far western Pacific. Also, while the zonal wind anomalies over the equatorial central Pacific are westerly, those over the equatorial far western Pacific are easterly. The nearly out-of-phase behavior between the eastern and western tropical Pacific is also observed during the cold phase of ENSO, but with anomalies of opposite sign. These western Pacific interannual anomaly patterns are robust features of ENSO, independent of data sets. It is argued that equatorial easterly (westerly) wind anomalies over the far western Pacific during the warm (cold) phase of ENSO are initiated by off-equatorial western Pacific cold (warm) SST anomalies, and that these winds are important for the evolution of ENSO. An atmosphere model is employed to demonstrate that small off-equatorial western Pacific cold (warm) SST anomalies (compared to those in the east) are sufficient to produce equatorial easterly (westerly) wind anomalies as observed over the far western Pacific. The coupled ocean-atmosphere model of Zebiak and Cane is then modified to investigate the evolution of the western Pacific interannual anomaly patterns in a coupled ocean-atmosphere system, by including a meridional structure to the subsurface temperature parameterization in the western Pacific. The modified model produces both western and eastern Pacific interannual anomaly patterns.
    Wang C. Z., W. Q. Wang, D. X. Wang, and Q. Wang, 2006: Interannual variability of the South China Sea associated with El Niño. J. Geophys. Res., 111,C03023, doi: 10.1029/2005JC 003333.
    Wang D. X., Q. Xie, Y. Du, W. Q. Wang, and J. Chen, 2002: The 1997-1998 warm event in the South China Sea. Chinese Science Bulletin, 47, 1221- 1227.10.1007/ strong warm event happens during spring 1997 to spring 1999 in the South China Sea. Its intensity and duration show that it is the strongest event on the record over the past decades. It also corresponds with the severe flood over the valley of the Yangtze River and a couple of marine environmental events. This note addressed the evolution process by using several data sets, such as sea surface temperature, height and wind stress in addition to subsurface temperature. The onset of the warm event almost teleconnects with the El Ni?o event in the tropical Pacific Ocean. Summer monsoon is stronger and winter monsoon is weaker in 1997 so that there are persistent westerly anomalies in the South China Sea. During the development phase, the warm advection caused by southerly anomalies is the major factor while the adjustment of the thermocline is not obvious. Subsequently, the southerly anomalies decay and even northerly anomalies appear in the summer of 1998 resulting from the weaker than normal summer monsoon in 1998 in the South China Sea. The thermocline develops deeper than normal, which causes the downwelling pattern and the start of the maintaining phase of the warm event. Temperature anomalies in the southern South China Sea begin to decay in the winter of 1998-1999 and this warm event ends in the May of 1999.
    Weare B. C., 1979: A statistical study of the relationships between ocean surface temperatures and the Indian monsoon. J. Atmos. Sci., 36, 2279- 2291.10.1175/1520-0469(1979)036<2279:ASSOTR>2.0.CO; The hypothesis that Indian Ocean sea surface temperatures are linked to the intensity of the Indian summer monsoon was tested using sea temperature, rainfall and sea level pressure data for the period 1949鈥72. The data sets were compacted using empirical orthogonal function analyses. The time coefficients of the most important functions were used to statistically test the general hypothesis. The results suggest that in summer a warmer Arabian Sea or Indian Ocean is weakly associated with decreased rainfall and increased sea level pressure over much of the Indian subcontinent. The relationship between the Indian summer monsoon and the sea surface temperatures of the eastern tropical Pacific Ocean was also investigated. This analysis suggests that higher than normal Indian sea level pressures are often associated with higher eastern Pacific sea temperatures one month later and higher Indian region sea temperatures another month later.
    Webster P. J., V. E. Toma, and H.-M. Kim, 2011: Were the 2010 Pakistan floods predictable? Geophys. Res. Lett., 38,L04806, doi: 10.1029/2010GL046346.10.1029/ July 2010, a series of monsoonal deluges over northern Pakistan resulted in catastrophic flooding, loss of life and property and an agricultural crisis that may last for years. Was the rainfall abnormal compared to previous years? Furthermore, could a high probability of flooding have been predicted? To address these questions, regional precipitation is analyzed using three dataset sets covering the 1981鈥2010 time period. It is concluded that the 2010 average May to August (MJJA) rainfall for year 2010 is somewhat greater in magnitude than previous years. However, the rainfall rate of the July deluges, especially in North Pakistan was exceptionally rare as deduced from limited data. The location of the deluges over the mountainous northern part of the country lead to the devastating floods. The European Centre for Medium Range Weather Forecasts (ECMWF) 15-day Ensemble Prediction System (EPS) is used to assess whether the rainfall over the flood affected region was predictable. A multi-year analysis shows that Pakistan rainfall is highly predictable out to 6鈥8 days including rainfall in the summer of 2010. We conclude that if these extended quantitative precipitation forecasts had been available in Pakistan, the high risk of flooding could have been foreseen. If these rainfall forecasts had been coupled to a hydrological model then the high risk of extensive and prolonged flooding could have anticipated and actions taken to mitigate their impact.
    Wittenberg A. T., A. Rosati, T. L. Delworth, G. A. Vecchi, and F. R. Zeng, 2014: ENSO modulation: Is it decadally predictable? J. Climate, 27, 2667- 2681.10.1175/ and climate simulations exhibit epochs of extreme El Ni脙卤o-Southern Oscillation (ENSO) behavior that can persist for decades. Previous studies have revealed a wide range of ENSO responses to forcings from greenhouse gases, aerosols, and orbital variations, but they have also shown that interdecadal modulation of ENSO can arise even without such forcings. The present study examines the predictability of this intrinsically generated component of ENSO modulation, using a 4000-yr unforced control run from a global coupled GCM [GFDL Climate Model, version 2.1 (CM2.1)] with a fairly realistic representation of ENSO. Extreme ENSO epochs from the unforced simulation are reforecast using the same ('perfect') model but slightly perturbed initial conditions. These 40-member reforecast ensembles display potential predictability of the ENSO trajectory, extending up to several years ahead. However, no decadal-scale predictability of ENSO behavior is found. This indicates that multidecadal epochs of extreme ENSO behavior can arise not only intrinsically but also delicately and entirely at random. Previous work had shown that CM2.1 generates strong, reasonably realistic, decadally predictable high-latitude climate signals, as well as tropical and extratropical decadal signals that interact with ENSO. However, those slow variations appear not to lend significant decadal predictability to this model's ENSO behavior, at least in the absence of external forcings. While the potential implications of these results are sobering for decadal predictability, they also offer an expedited approach to model evaluation and development, in which large ensembles of short runs are executed in parallel, to quickly and robustly evaluate simulations of ENSO. Further implications are discussed for decadal prediction, attribution of past and future ENSO variations, and societal vulnerability.
    Wu B., T. J. Zhou, and T. Li, 2009a: Contrast of rainfall-SST relationships in the western North Pacific between the ENSO-developing and ENSO-decaying summers. J. Climate, 22, 4398- 4405.10.1175/ the overall summer rainfall-sea surface temperature (SST) relationship has a negative correlation over the western North Pacific (WNP), this relationship experiences a significant interannual variation. During the ENSO-developing (decaying) summer, the rainfall-SST correlation is significantly positive (negative). The positive correlation is attributed to interplay between the anomalous W...
    Wu B., T. Li, and T. J. Zhou, 2010: Relative contributions of the Indian Ocean and local SST anomalies to the maintenance of the western North Pacific anomalous anticyclone during the El Niño decaying summer. J. Climate, 23, 2974- 2986.
    Wu G. X., H. Z. Liu, 1995: Neighborhood response of rainfall to tropical Sea surface temperature anomalies. Part I: numerical experiment. Chinese J. Atmos. Sci., 19, 422- 434. (in Chinese) response of rainfall to tropical sea surface temperature anomalies. Part I. Numerical experiment WU G.-X. Chinese J.Atmos.Sci. 19, 279-292, 1995
    Wu R. G., 2002: A mid-latitude Asian circulation anomaly pattern in boreal summer and its connection with the Indian and East Asian summer monsoons. Int. J. Climatol., 22, 1879- 1895.10.1002/ Using the NCEP&ndash;NCAR reanalysis for 1948&ndash;98, this study identifies a dominant pattern for the interannual variation of upper-level winds over mid-latitude Asia in boreal summer. This pattern, called the mid-latitude Asian summer (MAS) pattern, features two anomalous anticyclones: one centred at 37.5° N, 65° E and the other at 42.5° N, 130° E. The MAS pattern significantly influences East Asian summer monsoon variability. In the positive phase of the MAS pattern, contrasting meridional wind anomalies between eastern China and Japan lead to above- and below-normal summer rainfall in north China and south Japan respectively. The year-to-year change of the MAS pattern is related to that of the Indian summer rainfall, especially in central and northern India. Thus, the MAS pattern plays a role in connecting anomalous Indian heating with the East Asian summer monsoon variability.The East Asian anomalous anticyclone displays a southeastward shift after the late 1970s. This results in a similar change of anomalous summer rainfall regions in East Asia. The West Asian anomalous anticyclone moves northeastward after the late 1970s. The relation of the MAS pattern with the Indian summer rainfall experienced an obvious weakening in the late 1970s. As a result, the statistical relation between the Indian and north China summer rainfall becomes weak after the late 1970s. Copyright 08 2002 Royal Meteorological Society
    Wu R. G., B. Wang, 2002: A contrast of the East Asian summer monsoon-ENSO relationship between 1962-77 and 1978-93. J. Climate, 15, 3266- 3279.10.1175/1520-0442(2002)0152.0.CO; station rainfall data and the NCEP-NCAR reanalysis, the authors investigate changes in the interannual relationship between the east Asian summer monsoon (EASM) and El Ni01±o-Southern Oscillation (ENSO) in the late 1970s, concurrent with the Pacific climate shift. The present study focuses on decaying phases of ENSO because changes in developing phases of ENSO are less significant. Remarkable changes are found in the summer rainfall anomaly in northern China and Japan. From pre- to postshift period, the summer rainfall anomaly in eastern north China during decaying phases of El Ni01±o changed from above to below normal, whereas that in central Japan changed from negative to normal. Consistent with this, the barotropic anticyclonic anomaly over the Japan Sea changed to cyclonic; the associated anomalous winds changed from southerly to northerly over the Yellow Sea-northeastern China and from northeasterly to northwesterly over central Japan. The change in the ENSO-related east Asian summer circulation anomaly is attributed to changes in the location and intensity of anomalous convection over the western North Pacific (WNP) and India. After the late 1970s, the WNP convection anomaly is enhanced and shifted to higher latitudes due to increased summer mean SST in the Philippine Sea. This induces an eastward shift of an anomalous low pressure from east Asia to the North Pacific along 3000°-4500°N during decaying phases of El Ni01±o. Thus, anomalous winds over northeastern China and Korea switch from southeasterly to northeasterly. Before the late 1970s, an anomalous barotropic anticyclone develops over east Asia and anomalous southerties prevail over northeastern China during decaying phases of El Ni01±o. This may relate to anomalous Indian convection through a zonal wave pattern along 3000°-5000°N. After the late 1970s, anomalous Indian convection weakens, which reduces the impact of the Indian convection on the EASM.
    Wu R. G., Z. Z. Hu, and B. P. Kirtman, 2003: Evolution of ENSO-related rainfall anomalies in East Asia. J. Climate, 16, 3742- 3758.10.1175/1520-0442(2003)016<3742:EOERAI>2.0.CO; present study documents seasonal rainfall anomalies in East Asia during different phases of El Ni01±o09恪癝outhern Oscillation (ENSO) using station rainfall and the NCEP09恪癗CAR reanalysis for the period of 195109恪2000 through lag09恪發ead correlation/regression and extended singular value decomposition analyses. The ENSO-related rainfall anomalies consist of two major evolving centers of action: one positive and the other negative. The positive center of action affects southern China, eastern central China, and southern Japan during the fall of an ENSO developing year through the following spring. The negative center of action is over northern China during the summer and fall of an ENSO developing year. Seasonal rainfall variance explained by ENSO is about 20%09恪30% in southern China in fall and winter, about 20% in eastern central China in spring after the mature phase of ENSO, and around 15%09恪20% in western north China in summer and fall of an ENSO developing year. The two main rainfall anomalies are induced by different anomalous circulation systems. The positive center of action is closely related to an anomalous low-level anticyclone over the western North Pacific. The anomalous anticyclone develops over the South China Sea in fall and extends eastward in winter and moves northeastward in spring and summer. The evolution of this anticyclone is determined by large-scale equatorial heating anomalies and local air09恪皊ea interactions. The negative center of action in northern China is associated with an anomalous barotropic cyclone displacing southwestward along the East Asian coast during the developing stage of ENSO. Evolution of this cyclone is affected by anomalous heating over south Asia and the western North Pacific.
    Wu R. G., B. P. Kirtman, 2007: Regimes of seasonal air-sea interaction and implications for performance of forced simulations. Climate Dyn., 29, 393- 410.10.1007/ surface temperature (SST) anomalies can induce anomalous convection through surface evaporation and low-level moisture convergence. This SST forcing of the atmosphere is indicated in a positive local rainfall–SST correlation. Anomalous convection can feedback on SST through cloud-radiation and wind-evaporation effects and wind-induced oceanic mixing and upwelling. These atmospheric feedbacks are reflected in a negative local rainfall–SST tendency correlation. As such, the simultaneous rainfall–SST and rainfall–SST tendency correlations can indicate the nature of local air–sea interactions. Based on the magnitude of simultaneous rainfall–SST and rainfall–SST tendency correlations, the present study identifies three distinct regimes of local air–sea interactions. The relative importance of SST forcing and atmospheric forcing differs in these regimes. In the equatorial central-eastern Pacific and, to a smaller degree, in the western equatorial Indian Ocean, SST forcing dominates throughout the year and the surface heat flux acts mainly as a damping term. In the tropical Indo-western Pacific Ocean regions, SST forcing and atmospheric forcing dominate alternatively in different seasons. Atmospheric forcing dominates in the local warm/rainy season. SST forcing dominates with a positive wind-evaporation feedback during the transition to the cold/dry season. SST forcing also dominates during the transition to the warm/rainy season but with a negative cloud-radiation feedback. The performance of atmospheric general circulation model simulations forced by observed SST is closely linked to the regime of air–sea interaction. The forced simulations have good performance when SST forcing dominates. The performance is low or poor when atmospheric forcing dominates.
    Wu R. G., B. P. Kirtman, V. Krishnamurthy, 2008: An asymmetric mode of tropical Indian Ocean rainfall variability in boreal spring. J. Geophys. Res., 113(D5),D05104, doi: 10.1029/2007JD 009316.10.1029/[1] An analysis of observational estimates has revealed an asymmetric mode of boreal spring rainfall and wind variability over the tropical Indian Ocean. The asymmetric mode is characterized by opposite rainfall and surface wind anomalies north and south of the equator. This mode is associated with a cross-equatorial gradient in sea surface temperature anomalies. The evolution of this mode is related to air-sea interactions in the tropical Indian Ocean. In particular, surface heat fluxes play an important role in the initiation, development, and decay of this mode. The occurrence of this mode in observations is closely linked to both El Nino-Southern Oscillation (ENSO) and the Indian Ocean Dipole mode. Coupled general circulation model experiments indicate that this mode can occur in the absence of ENSO. The variability associated with this mode enhances ENSO's teleconnection to the Indian Ocean and affects the seasonal transition in the tropical Indian Ocean.
    Wu R. G., G. Huang, Z. C. Du, and K. M. Hu, 2014: Cross-season relation of the South China Sea precipitation variability between winter and summer. Climate Dyn., 43, 193- 207.10.1007/ present study reveals cross-season connections of rainfall variability in the South China Sea (SCS) region between winter and summer. Rainfall anomalies over northern South China Sea in boreal summer tend to be preceded by the same sign rainfall anomalies over southern South China Sea in boreal winter (denoted as in-phase relation) and succeeded by opposite sign rainfall anomalies over southern South China Sea in the following winter (denoted as out-of-phase relation). Analysis shows that the in-phase relation from winter to summer occurs more often in El Ni09o/La Ni09a decaying years and the out-of-phase relation from summer to winter appears more frequently in El Ni09o/La Ni09a developing years. In the summer during the El Ni09o/La Ni09a decaying years, cold/warm and warm/cold sea surface temperature (SST) anomalies develop in tropical central North Pacific and the North Indian Ocean, respectively, forming an east–west contrast pattern. The in-phase relation is associated with the influence of anomalous heating/cooling over the equatorial central Pacific during the mature phase of El Ni09o/La Ni09a events that suppresses/enhances precipitation over southern South China Sea and the impact of the above east–west SST anomaly pattern that reduces/increases precipitation over northern South China Sea during the following summer. The impact of the east–west contrast SST anomaly pattern is confirmed by numerical experiments with specified SST anomalies. In the El Ni09o/La Ni09a developing years, regional air-sea interactions induce cold/warm SST anomalies in the equatorial western North Pacific. The out-of-phase relation is associated with a Rossby wave type response to anomalous heating/cooling over the equatorial central Pacific during summer and the combined effect of warm/cold SST anomalies in the equatorial central Pacific and cold/warm SST anomalies in the western North Pacific during the mature phase of El Ni09o/La Ni09a events.
    Wu Z. W., B. Wang, J. P. Li, and F.-F. Jin, 2009b: An empirical seasonal prediction model of the East Asian summer monsoon using ENSO and NAO. J. Geophys. Res.,114, doi: 10.1029/2009JD011733.
    Xiang B. Q., B. Wang, W. D. Yu, and S. B. Xu, 2013: How can anomalous western North Pacific subtropical high intensify in late summer? Geophys. Res. Lett., 40, 2349- 2354.10.1002/ [1] The western North Pacific (WNP) Subtropical High (WNPSH) is a controlling system for East Asian Summer monsoon and tropical storm activities, whereas what maintains the anomalous summertime WNPSH has been a long-standing riddle. Here we demonstrate that the local convection-wind-evaporation-SST (CWES) feedback relying on both mean flows and mean precipitation is key in maintaining the WNPSH, while the remote forcing from the development of the El Nino/Southern Oscillation is secondary. Strikingly, the majority of strong WNPSH cases exhibit anomalous intensification in late summer (August), which is dominantly determined by the seasonal march of the mean state. That is, enhanced mean precipitation associated with strong WNP monsoon trough in late summer makes atmospheric response much more sensitive to local SST forcing than early summer.
    Xie P. P., P. A. Arkin, 1997: Global precipitation: A 17-year monthly analysis based on gauge observations, satellite estimates, and numerical model outputs. Bull. Amer. Meteor. Soc., 78, 2539- 2558.10.1175/1520-0477(1997)078<2539:GPAYMA>2.0.CO; Gridded fields (analyses) of global monthly precipitation have been constructed on a 2.5° latitude–longitude grid for the 17-yr period from 1979 to 1995 by merging several kinds of information sources with different characteristics, including gauge observations, estimates inferred from a variety of satellite observations, and the NCEP–NCAR reanalysis. This new dataset, which the authors have named the CPC Merged Analysis of Precipitation (CMAP), contains precipitation distributions with full global coverage and improved quality compared to the individual data sources. Examinations showed no discontinuity during the 17-yr period, despite the different data sources used for the different subperiods. Comparisons of the CMAP with the merged analysis of Huffman et al. revealed remarkable agreements over the global land areas and over tropical and subtropical oceanic areas, with differences observed over extratropical oceanic areas. The 17-yr CMAP dataset is used to investigate the annual and interannual variability in large-scale precipitation. The mean distribution and the annual cycle in the 17-yr dataset exhibit reasonable agreement with existing long-term means except over the eastern tropical Pacific. The interannual variability associated with the El Ni09o–Southern Oscillation phenomenon resembles that found in previous studies, but with substantial additional details, particularly over the oceans. With complete global coverage, extended period and improved quality, the 17-yr dataset of the CMAP provides very useful information for climate analysis, numerical model validation, hydrological research, and many other applications. Further work is under way to improve the quality, extend the temporal coverage, and to refine the resolution of the merged analysis.
    Xie S.-P., S. G. H. Philander, 1994: A coupled ocean-atmosphere model of relevance to the ITCZ in the eastern Pacific. Tellus,46, doi: 10.1034/j.1600-0870.1994.t01-1-00001.x.10.1034/ The intertropical convergence zone (ITCZ) stays in the northern hemisphere over the Atlantic and eastern Pacific, even though the annual mean position of the sun is on the equator. To study some processes that contribute to this asymmetry about the equator, we use a two-dimensional model which neglects zonal variations and consists of an ocean model with a mixed layer coupled to a simple atmospheric model. In this coupled model, the atmosphere not only transports momentum into the ocean, but also directly affects sea surface temperature by means of wind stirring and surface latent heat flux. Under equatorially symmetric conditions, the model has, in addition to an equatorially symmetric solution, two asymmetric solutions with a single ITCZ that forms in only one hemisphere. Strong equatorial upwelling is essential for the asymmetry. Local oceanic turbulent processes involving vertical mixing and surface latent heat flux, which are dependent on wind speed, also contribute to the asymmetry.
    Xie S.-P., H. Annamalai, F. A. Schott, and J. P. McCreary Jr., 2002: Structure and mechanisms of South Indian Ocean climate variability. J. Climate, 15, 864-
    Xie S.-P., Q. Xie, D. X. Wang, and W. T. Liu, 2003: Summer upwelling in the South China Sea and its role in regional climate variations. J. Geophys. Res., 108,3261, doi: 10.1029/2003JC001867.10.1029/ and interannual variations of summer upwelling off the South Vietnam coast and the offshore spread of cold water are investigated using a suite of new satellite measurements. In summer, as the southwesterly winds impinge on Annam Cordillera (a north-south running mountain range on the east coast of Indochina) a strong wind jet occurs at its southern tip offshore east of Saigon, resulting in strong wind curls that are important for ocean upwelling off the coast. In July and August an anticyclonic ocean eddy develops to the southeast, advecting the cold coastal water offshore into the open South China Sea (SCS). The center of this cold filament is located consistently north of the wind speed maximum, indicating that open-ocean upwelling helps to cool the ocean surface. Corroborating evidence for the cold filament is found in ocean color observations that reveal a collocated tongue of high chlorophyll concentration. The development of this cold filament disrupts the summer warming of the SCS and causes a pronounced semiannual cycle in SST. Moreover, the cold filament is an important player in interannual variability in the summer SCS. In 1998, the cold filament and mid-summer cooling never took place, giving rise to a strong basin-wide surface warming. Interannual SST variance has a local maximum over the climatological cold filament, and is much greater than the variance over the adjacent Indian and western Pacific Oceans. A cold filament index is constructed, which displays significant lagged correlation with SST in the eastern equatorial Pacific and Indian Oceans, indicative of a teleconnection from El Nino.
    Xie S.-P., K. M. Hu, J. Hafner, H. Tokinaga, Y. Du, G. Huang, and T. Sampe, 2009: Indian Ocean capacitor effect on Indo-western Pacific climate during the summer following El Niño. J. Climate, 22, 730- 747.
    Xie S.-P., Y. Du, G. Huang, X.-T. Zheng, H. Tokinaga, K. M. Hu, and Q. Y. Liu, 2010: Decadal shift in El Niño influences on Indo-Western Pacific and East Asian climate in the 1970s. J. Climate, 23, 3352- 3368.10.1175/ El Ni09o’s influence on the subtropical northwest (NW) Pacific climate increased after the climate regime shift of the 1970s. This is manifested in well-organized atmospheric anomalies of suppressed convection and a surface anticyclone during the summer (June–August) of the El Ni09o decay year [JJA(1)], a season when equatorial Pacific sea surface temperature (SST) anomalies have dissipated. In situ observations and ocean–atmospheric reanalyses are used to investigate mechanisms for the interdecadal change. During JJA(1), the influence of the El Ni09o–Southern Oscillation (ENSO) on the NW Pacific is indirect, being mediated by SST conditions over the tropical Indian Ocean (TIO). The results here show that interdecadal change in this influence is due to changes in the TIO response to ENSO. During the postregime shift epoch, the El Ni09o teleconnection excites downwelling Rossby waves in the south TIO by anticyclonic wind curls. These Rossby waves propagate slowly westward, causing persistent SST warming over the thermocline ridge in the southwest TIO. The ocean warming induces an antisymmetric wind pattern across the equator, and the anomalous northeasterlies cause the north Indian Ocean to warm through JJA(1) by reducing the southwesterly monsoon winds. The TIO warming excites a warm Kelvin wave in tropospheric temperature, resulting in robust atmospheric anomalies over the NW Pacific that include the surface anticyclone. During the preregime shift epoch, ENSO is significantly weaker in variance and decays earlier than during the recent epoch. Compared to the epoch after the mid-1970s, SST and wind anomalies over the TIO are similar during the developing and mature phases of ENSO but are very weak during the decay phase. Specifically, the southern TIO Rossby waves are weaker, so are the antisymmetric wind pattern and the North Indian Ocean warming during JJA(1). Without the anchor in the TIO warming, atmospheric anomalies over the NW Pacific fail to develop during JJA(1) prior to the mid-1970s. The relationship of the interdecadal change to global warming and implications for the East Asian summer monsoon are discussed.
    Xie S.-P., Coauthors , 2015: Towards predictive understanding of regional climate change. Nature Clim.Change, 5, 921- 930.10.1038/ information on climate change is urgently needed but often deemed unreliable. To achieve credible regional climate projections, it is essential to understand underlyingphysical processes, reduce model biases and evaluate their impact on projections, andadequately account for internal variability. In the tropics, where atmospheric internalvariability is small compared to the forced change, advancing our understanding of thelong-term coupling between changes in upper ocean temperature and the atmosphericcirculation will help most to narrow uncertainty. In the extratropics, relatively largeinternal variability introduces substantial uncertainty, while exacerbating risks associated with extreme events. Large ensemble simulations are essential to estimate theprobabilistic distribution of climate change on regional scales. We conclude that thecurrent priority is to understand and reduce uncertainties on scales > 100 km to facilitate assessments at finer scales.
    Yamaura T., T. Tomita, 2011: Spatiotemporal differences in the interannual variability of Baiu frontal activity in June. Int. J. Climatol., 31, 57- 71.10.1002/ The Baiu frontal activity (BFA) clearly shows spatiotemporal differences in its interannual variability. This work examines the physical mechanisms behind these differences. On interannual time scales, the Baiu front can be divided into three subregions: (1) the western Baiu (WB), (2) the central Baiu (CB), and (3) the eastern Baiu (EB). Time series analysis revealed that the dominant periods in these three subregions are long eastward periods of approximately 2 years in the WB, 4 years in the CB, and 6 years in the EB. The biennial oscillation of the Asian monsoon controls the interannual variation in the WB through specific meridional circulation in the western North Pacific, whereas the El Nino/Southern Oscillation forces the interannual variation in the CB through the Pacific ast Asian teleconnection. The interannual variation in the EB is controlled by mid-latitude atmospheric circulations, not by effects from the Tropics. The summertime North Atlantic Oscillation (SNAO) with a 6-year period excites the stationary Rossby waves, the energies of which reach Japan through the strong upper tropospheric westerlies over Eurasia. Geopotential height anomalies then appear around Japan with an equivalent barotropic structure that modifies the precipitation in the EB. Copyright 2009 Royal Meteorological Society
    Yang J. L., Q. Y. Liu, S.-P. Xie, Z. Y. Liu, and L. X. Wu, 2007: Impact of the Indian Ocean SST basin mode on the Asian summer monsoon. Geophys. Res. Lett., 34,L02708, doi: 10.10029/2006GL028571.10.1029/ 1] Following an El Nino event, a basin-wide warming takes place over the tropical Indian Ocean, peaks in late boreal winter and early spring, and persists through boreal summer. Our observational analysis suggests that this Indian Ocean warming induces robust climatic anomalies in the summer Indo-West Pacific region, prolonging the El Nino's influence after tropical East Pacific sea surface temperature has returned to normal. In response to the Indian Ocean warming, precipitation increases over most of the basin, forcing a Matsuno-Gill pattern in the upper troposphere with a strengthened South Asian high. Near the ground, the southwest monsoon intensifies over the Arabian Sea and weakens over the South China and Philippine Seas. An anomalous anticyclonic circulation forms over the subtropical Northwest Pacific, collocated with negative precipitation anomalies. All these anomaly patterns are reproduced in a coupled model simulation initialized with a warming in the tropical Indian Ocean mixed layer, indicating that the Indian Ocean warming is not just a passive response to El Nino but important for summer climate variability in the Indo-West Pacific region. The implications for seasonal prediction are discussed.
    Yang Y. L., S.-P. Xie, Y. Du, and H. Tokinaga, 2015: Interdecadal difference of interannual variability characteristics of South China Sea SSTs associated with ENSO. J. Climate, 28, 7145- 7160.10.1175/ correlation between sea surface temperature (SST) and El Ni脙卤o-Southern Oscillation (ENSO) persists into post-ENSO September over the South China Sea (SCS), the longest correlation in the World Ocean. Slow modulations of this correlation are analyzed by using the International Comprehensive Ocean-Atmosphere Dataset (ICOADS). ENSO's influence on SCS SST has experienced significant interdecadal changes over the past 138 years (1870-2007), with a double-peak structure correlation after the 1960s compared to a single-peak before the 1940s. According to the ENSO correlation character, the analysis period is divided into four epochs. In epoch 3, 1960-83, the SST warming and enhanced precipitation over the southeastern tropical Indian Ocean, rather than the Indian Ocean basinwide warming, induce easterly wind anomalies and warm up the SCS in the summer following El Ni脙卤o. Besides the Indian Ocean effect, during epochs 2 (1930-40) and 4 (1984-2007), the Pacific-Japan (PJ) pattern of atmospheric circulation anomalies helps sustain the SCS SST warming through summer (June-August) with easterly wind anomalies. The associated increase in shortwave radiation and decrease in upward latent heat flux cause the SCS SST warming to persist into the summer. Meanwhile, the rainfall response around the SCS to ENSO shows interdecadal variability, with stronger variability after the 1980s. The results suggest that both the remote forcing from the tropical Indian Ocean and the PJ pattern are important for the ENSO teleconnection to the SCS and its interdecadal modulations.
    Yasunaka S., K. Hanawa, 2006: Interannual summer temperature variations over Japan and their relation to large-scale atmospheric circulation field. J. Meteor. Soc.Japan, 84, 641- 652.10.2151/ modes of surface air temperature (SAT) interannual variations in Japanese summer climate are detected by a rotated empirical orthogonal function analysis, and statistical relations between the dominant SAT modes and atmospheric circulation are investigated by regression analyses. Relations to the large-scale atmospheric circulation patterns that had been already known, are also examined. As a result, two dominant modes are detected that correspond well to the large-scale atmospheric circulation patterns, and relations between the SAT modes and atmospheric circulation can be interpreted statistically. The first mode represents SAT variations in the central part of Japan. The second mode represents those in the northern part. Greater than 75% of SAT variations can be explained by these two leading modes. The first mode accompanies variations of sunshine duration, and is related with the strength of the Tibetan High. The second mode involves quasi-six-year periodicity, and accompanies an appearance of the shallow type of the Okhotsk High, with the cold northeasterly winds that is related with the convective activity around the Philippine Islands.
    Ye H., R. Y. Lu, 2011: Subseasonal variation in ENSO-related East Asian rainfall anomalies during summer and its role in weakening the relationship between the ENSO and summer rainfall in eastern China since the late 1970s. J. Climate, 24, 2271- 2284.10.1175/ The findings of the study reported in this paper show that, during ENSO decaying summers, rainfall and circulation anomalies exhibit clear subseasonal variation. Corresponding to a positive (negative) December-February (DJF) Nino-3.4 index, a positive (negative) subtropical rainfall anomaly, with a southwest-northeast tilt, appears in South China and the western North Pacific (WNP) in the subsequent early summer (from June to middle July) but advances northward into the Huai River Basin in China as well as Korea and central Japan in late summer (from late July to August). Concurrently, a lower-tropospheric anticyclonic anomaly over the WNP extends northward from early to late summer. The seasonal change in the basic flows, characterized by the northward shift of the upper-tropospheric westerly jet and the WNP subtropical high, is suggested to be responsible for the differences in the above rainfall and circulation anomalies between early and late summer by inducing distinct extratropical responses even under the almost identical tropical forcing of a precipitation anomaly in the Philippine Sea. A particular focus of the study is to investigate, using station rainfall data, the subseasonal variations in ENSO-related rainfall anomalies in eastern China since the 1950s, to attempt to examine their role in weakening the relationship between the ENSO and summer mean rainfall in eastern China since the late 1970s. It is found that the ENSO-related rainfall anomalies tend to be similar between early and late summer before the late 1970s, that is, the period characterized by a stronger ENSO-summer mean rainfall relationship. After the late 1970s, however, the anomalous rainfall pattern in eastern China is almost reversed between early and late summer, resulting accordingly in a weakened relationship between the ENSO and total summer rainfall in eastern China.
    Yu J. H., T. Li, Z. M. Tan, and Z. W. Zhu, 2015: Effects of tropical North Atlantic SST on tropical cyclone genesis in the western North Pacific. Climate Dyn., doi: 10.1007/s00382-015-2618-x.10.1007/ tropical cyclone genesis number (TCGN) in July–October (JASO) over the western North Pacific (WNP) exhibits a robust interannual variation. It shows a longitudinally tri-pole pattern with a high in the eastern WNP and South China Sea (SCS) and a low in the western WNP, which explain 42.2 and 23.402% of total TCGN variance in the eastern WNP and SCS, respectively. The high–low–high pattern is similar to that derived from a TC genesis potential index (GPI). To understand the cause of the longitudinal distribution of the dominant interannual mode, we examine the contributions of environmental parameters associated with GPI. It is found that relative humidity and relative vorticity are important factors responsible for TC variability in the SCS, while vertical shear and relative vorticity are crucial in determining TC activity in eastern WNP. A simultaneous correlation analysis shows that the WNP TCGN in JASO is significantly negatively correlated (with a correlation coefficient of 610.5) with sea surface temperature anomalies (SSTA) in the tropical North Atlantic (TNA). The longitudinal distribution of TC genesis frequency regressed onto TNA SSTA resembles that regressed upon the WNP TCGN series. The spatial patterns of regressed environmental variables onto the SSTA over the TNA also resemble those onto TCGN in the WNP, that is, an increase of relative humidity in the SCS and a weakening of vertical shear in the eastern WNP are all associated with cold SSTA in the TNA. Further analyses show that the cold SSTA in the TNA induce a negative heating in situ. In response to this negative heating, a low (upper)-level anomalous aniti-cyclonic (cyclonic) flows appear over the subtropical North Atlantic and eastern North Pacific, and to east of the cold SSTA, anomalous low-level westerlies appear in the tropical Indian Ocean. Given pronounced mean westerlies in northern Indian Ocean in boreal summer, the anomalous westerly flows increase local surface wind speed and surface evaporation and cool the SST in situ. Cold SSTA in northern Indian Ocean further suppress local convection, inducing anomalous westerlies to its east, leading to enhanced cyclonic vorticity and low surface pressure over the WNP monsoon trough region. Idealized numerical experiments further confirm this Indian Ocean relaying effect, through which cold SSTA in the tropical Atlantic exert a remote impact to circulation in the WNP.
    Yuan Y., S. Yang, 2012: Impacts of different types of El Niño on the East Asian climate: Focus on ENSO cycles. J Climate, 25, 7702-
    Yun K.-S., S.-W. Yeh, and K.-J. Ha, 2013: Distinct impact of tropical SSTs on summer North Pacific high and western North Pacific subtropical high. J. Geophys. Res. Atmos., 118, 4107- 4116.10.1002/ [1] The distinct impact of tropical Indian Ocean (IO) and western Pacific (WP) sea surface temperatures (SSTs) after the El Nino winter has been investigated in relation to the summer North Pacific high (NPH) and western North Pacific subtropical high (WNPSH). After the El Nino winter, warming of the IO leads to a summer eastern Pacific (EP) SST anomaly distinct from the cooling of WP; EP cooling occurs in the extreme IO warming case and EP warming in the WP cooling case. Both the warming of the IO and cooling of the WP are responsible for the development of the WNPSH, whereas the summer EP cooling induces an enhanced NPH, especially if it coexists with IO warming. The IO warming triggers an abrupt termination of the El Nino event by causing the easterly anomaly in the WP, which leads to the coexistence of IO warming and EP cooling during the boreal summer. The tropical EP cooling may change the North Pacific SST anomalies via the atmospheric bridge and consequently strengthen the extratropical NPH. The experimental results, which have been obtained from the use of atmospheric general circulation model, support the distinct roles of EP cooling on the NPH and of IO warming and WP cooling on the WNPSH. This finding suggests that the combined effect of IO warming and EP cooling generates a coupled pattern of NPH and WNPSH.
    Zhan R. F., Y. Q. Wang, and C.-C. Wu, 2011: Impact of SSTA in the East Indian Ocean on the frequency of Northwest Pacific tropical cyclones: A regional atmospheric model study. J. Climate, 24, 6227-
    Zhang R. H., A. Sumi, and M. Kimoto, 1996: Impact of El Niño on the East Asian monsoon: A diagnostic study of the '86/87 and '91/92 events. J. Meteor. Soc.Japan, 74, 49-'8687_and_'9192_eventsABSTRACT
    Zheng X. T., S.-P. Xie, and Q. Y. Liu, 2011: Response of the Indian Ocean Basin mode and its capacitor effect to global warming. J. Climate, 24, 6146- 6164.10.1175/ The development of the Indian Ocean basin (IOB) mode and its change under global warming are investigated using a pair of integrations with the Geophysical Fluid Dynamics Laboratory Climate Model version 2.1 (CM2.1). In the simulation under constant climate forcing, the El Ni09o–induced warming over the tropical Indian Ocean (TIO) and its capacitor effect on summer northwest Pacific climate are reproduced realistically. In the simulation forced by increased greenhouse gas concentrations, the IOB mode and its summer capacitor effect are enhanced in persistence following El Ni09o, even though the ENSO itself weakens in response to global warming. In the prior spring, an antisymmetric pattern of rainfall–wind anomalies and the meridional SST gradient across the equator strengthen via increased wind–evaporation–sea surface temperature (WES) feedback. ENSO decays slightly faster in global warming. During the summer following El Ni09o decay, the resultant decrease in equatorial Pacific SST strengthens the SST contrast with the enhanced TIO warming, increasing the sea level pressure gradient and intensifying the anomalous anticyclone over the northwest Pacific. The easterly wind anomalies associated with the northwest Pacific anticyclone in turn sustain the SST warming over the north Indian Ocean and South China Sea. Thus, the increased TIO capacitor effect is due to enhanced air–sea interaction over the TIO and with the western Pacific. The implications for the observed intensification of the IOB mode and its capacitor effect after the 1970s are discussed.
    Zheng X.-T., S.-P. Xie, Y. Du, L. Liu, G. Huang, and Q. Y. Liu, 2013: Indian Ocean Dipole response to global warming in the CMIP5 multimodel ensemble. J. Climate, 26, 6067- 6080.10.1175/ The response of the Indian Ocean dipole (IOD) mode to global warming is investigated based on simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5). In response to increased greenhouse gases, an IOD-like warming pattern appears in the equatorial Indian Ocean, with reduced (enhanced) warming in the east (west), an easterly wind trend, and thermocline shoaling in the east. Despite a shoaling thermocline and strengthened thermocline feedback in the eastern equatorial Indian Ocean, the interannual variance of the IOD mode remains largely unchanged in sea surface temperature (SST) as atmospheric feedback and zonal wind variance weaken under global warming. The negative skewness in eastern Indian Ocean SST is reduced as a result of the shoaling thermocline. The change in interannual IOD variance exhibits some variability among models, and this intermodel variability is correlated with the change in thermocline feedback. The results herein illustrate that mean state changes modulate interannual modes, and suggest that recent changes in the IOD mode are likely due to natural variations.
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Manuscript received: 05 August 2015
Manuscript revised: 23 October 2015
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Indo-Western Pacific Ocean Capacitor and Coherent Climate Anomalies in Post-ENSO Summer: A Review

  • 1. Scripps Institution of Oceanography, University of California San Diego, La Jolla, California 92093-0206, USA
  • 2. Physical Oceanography Laboratory/Qingdao Collaborative Innovation Center of Marine Science and Technology, Ocean University of China, Qingdao, Shandong 266100
  • 3. Research Center for Advanced Science and Technology, University of Tokyo, Tokyo 153-8904, Japan
  • 4. State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301
  • 5. State key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics and Center for Monsoon System Research, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029
  • 6. Indian Institute of Tropical Meteorology, Pune 411 008, India

Abstract: ENSO induces coherent climate anomalies over the Indo-western Pacific, but these anomalies outlast SST anomalies of the equatorial Pacific by a season, with major effects on the Asian summer monsoon. This review provides historical accounts of major milestones and synthesizes recent advances in the endeavor to understand summer variability over the Indo-Northwest Pacific region. Specifically, a large-scale anomalous anticyclone (AAC) is a recurrent pattern in post-El Niño summers, spanning the tropical Northwest Pacific and North Indian oceans. Regarding the ocean memory that anchors the summer AAC, competing hypotheses emphasize either SST cooling in the easterly trade wind regime of the Northwest Pacific or SST warming in the westerly monsoon regime of the North Indian Ocean. Our synthesis reveals a coupled ocean-atmosphere mode that builds on both mechanisms in a two-stage evolution. In spring, when the northeast trades prevail, the AAC and Northwest Pacific cooling are coupled via wind-evaporation-SST feedback. The Northwest Pacific cooling persists to trigger a summer feedback that arises from the interaction of the AAC and North Indian Ocean warming, enabled by the westerly monsoon wind regime. This Indo-western Pacific ocean capacitor (IPOC) effect explains why El Niño stages its last act over the monsoonal Indo-Northwest Pacific and casts the Indian Ocean warming and AAC in leading roles. The IPOC displays interdecadal modulations by the ENSO variance cycle, significantly correlated with ENSO at the turn of the 20th century and after the 1970s, but not in between. Outstanding issues, including future climate projections, are also discussed.

1. Introduction
  • ENSO is the dominant mode of interannual variability. Arising from Pacific ocean-atmosphere interaction, ENSO affects climate around the globe through atmospheric teleconnections and by inducing SST responses in other ocean basins. The atmospheric response to SST anomalies in the tropical Pacific has been extensively studied, including the Pacific-North American (PNA) teleconnection pattern (Trenberth et al., 1998; Alexander et al., 2002). Not as well-known but of regional importance are ENSO-correlated climate anomalies after ENSO has peaked. Here, we focus on the summer climate of the Indo-Northwest Pacific region, which encompasses South, Southeast and East Asia, home to more than three billion people. Summer is the rainy season for the Asian monsoon region, often accounting for more than 50% of the annual precipitation. The leading EOF mode of summer rainfall variability in the Indo-Northwest Pacific region (north of 10°N) is significantly correlated with ENSO——not concurrently, but at a two-season lag. Such pronounced climate anomalies develop in post-ENSO summers when equatorial Pacific SST anomalies have largely dissipated. Our review tells the story of how these anomalies were identified, and their patterns and mechanisms unraveled.

    Figure 1.  Summer (JJA) climatology over the Indo-western Pacific for 1979-2014: SST (black contours; interval $=1^\circ$C; thick contours for 10$^\circ$C, 15$^\circ$C, 20$^\circ$C and 25$^\circ$C and dashed contours for 29.5$^\circ$C), precipitation (gray shading representing $>$5 mm d$^-1$, and white contours for $7,9,11,\ldots$ mm d$^-1$), and surface wind velocity (arrows, m s$^-1$) [based on ERSST.v3b (Smith et al. 2008), CMAP (Xie and Arkin, 1997) and JRA-55 (Kobayashi et al., 2015)].

    In summer, the Indo-Northwest Pacific oceans are occupied by some of the warmest water of the global ocean. SST generally exceeds 28°C or even 29°C, except in the western Arabian Sea and during intraseasonal upwelling events off South Vietnam in the South China Sea (SCS). Atmospheric convection is active over this Indo-Northwest Pacific warm pool, organized into several regional centers (off the west coast of India, in the Bay of Bengal and SCS; Fig. 1). The southwest monsoon winds prevail from the Arabian Sea through the SCS up to 140°E, while the easterly trade winds prevail to the east. The division of the westerly monsoon and easterly trade wind regimes proves important for SST variability, as will become clear. Over East Asia, there is a northeastward-slanted rain band called Mei-yu in China, Changma in Korea, and Baiu in Japan. It brings the rainy season and is the single most important climate phenomenon to the region (Ding and Chan, 2005). ENSO is a major driver for climate variability over the Indo-Northwest Pacific region.

    ENSO is phase-locked to the annual cycle. Typically, eastern Pacific (Niño3.4) SST anomalies begin to develop in June-August [JJA(0)], peak in December(0), and decay rapidly in April(1) (Fig. 2a). Here, the numerals in parentheses denote the ENSO developing (0) and decay (1) years. Seasons refer to those in the NH. Compared to the well-known concurrent [JJA(0)] anomalies of the Indian summer monsoon that are anchored by tropical Pacific SST anomalies, JJA(1) anomalies in the atmosphere may seem peculiar without robust Niño3.4 SST anomalies, but are well documented. Over the tropical Northwest (TNW) Pacific, rainfall variability is better correlated with ENSO in JJA(1) than JJA(0) (Fig. 2b), and there are fewer tropical cyclones (TCs) in post-El Niño summers (Du et al., 2011). These JJA(1) atmospheric anomalies are consistent with the result of (Harrison and Larkin, 1996) that ENSO-induced anomalies of SLP last through September(1) over the TNW Pacific, the longest persistence in their surface meteorological analysis. The long-lasting SLP anomalies turn out to be part of a large-scale anomalous anticyclone over the TNW Pacific, which develops at the peak of El Niño and persists through JJA(1) (Wang et al., 2003). The summer anomalous anticyclone (AAC) is associated with suppressed local convection and part of the Pacific-Japan (PJ) pattern (Nitta, 1986) identified originally from analysis of reflective cloud cover.

    The identification of the AAC development following El Niño is a major advance in Asian monsoon research. The AAC affects the East Asian summer monsoon to the north (Huang and Wu, 1989; Chang et al., 2000) via the PJ pattern and the Indian summer monsoon to the west (Mishra et al., 2012). In post-ENSO summers without robust SST anomalies in the equatorial Pacific, the recurrent AAC must be anchored by ocean memory elsewhere. Identifying this ocean memory proved not straightforward and took many turns. The initial search naturally focused on the TNW Pacific, but with mixed results (Nitta, 1987). (Wang et al., 2000) proposed a wind-evaporation-SST (WES) feedback mechanism acting on the prevailing winter northeasterly monsoon winds. The challenge is how to apply this winter mechanism to summer when the northeast trade wind regime retreats east of 140°E (Fig. 1).

    In JJA(1), the most robust El Niño-induced SST anomalies of the global ocean are found in the tropical Indian Ocean (IO) and SCS. It is well known that the tropical IO warms up a season after El Niño (Weare, 1979) but the IO warming has previously been viewed as a passive response to El Niño without a climatic effect. This idea is supported by the observations that in the developing and mature stages of El Niño, atmospheric convection is suppressed, instead of being energized, over the warming tropical IO. The second difficulty in invoking SST anomalies in the IO-TNW Pacific warm pool as the ocean memory for JJA(1) atmospheric anomalies is the fact that the local SST-precipitation relationship is weak in the region (Wang et al., 2005; Wu and Kirtman, 2007). This difficulty notwithstanding, observational analysis reveals a (Matsuno, 1966)-(Gill, 1980) pattern in the free troposphere that is consistent with the forcing by a warming IO and can give rise to an AAC over the TNW Pacific (Xie et al., 2009). Modeling studies support this IO forcing of the TNW Pacific AAC (Wu and Liu, 1995; Li et al., 2008; Huang et al., 2010; Wu et al., 2010; Chowdary et al., 2011).

    The perception that the tropical IO is largely passive also stems from the observational result that the North IO response to ENSO can be largely explained from surface heat flux adjustments (via the cloud radiative effect and wind-induced latent heat flux) without invoking ocean dynamics. Challenging this passive IO view is the recent observational result that the SST response to El Niño features two peaks over the North IO (Du et al., 2009) and SCS (Wang et al., 2006); the first peak coincides with the peak phase of El Niño but the second one is in the post-El Niño summer (Fig. 2a). The summer peak is peculiar as it cannot be forced directly by El Niño. Instead, it results from positive feedback of the Indo-TNW Pacific ocean-atmosphere interaction that prolongs the response to El Niño (Du et al., 2009; Kosaka et al., 2013; Wang et al., 2013). In a post-El Niño summer, JJA(1), the North IO is kept warm by the anomalous easterlies on the south flank of the TNW Pacific AAC, which oppose the prevailing southwest monsoon and reduce surface evaporation (Du et al., 2009). Meanwhile, the North IO warming anchors the AAC via an atmospheric Kelvin wave adjustment (Xie et al., 2009). This new coupled mode of Indo-TNW Pacific cross-basin interaction explains why ENSO anomalies last longest over the Indo-TNW Pacific and the AAC is the preferred pattern (Kosaka et al., 2013). This is analogous to the Indian Ocean dipole (IOD) mode (Saji et al., 1999), which is excited by El Niño but takes up a distinctive pattern characteristic of Bjerknes feedback.

    Major advances have been made in describing and explaining post-ENSO ocean-atmospheric anomalies over the Indo-TNW Pacific warm pool. A new paradigm is emerging that depicts an IO that is more dynamically and climatically active than previously thought. It reveals a new kind of inter-basin interaction between the tropical IO and TNW Pacific mediated by the AAC. Elements of the paradigm have been published over more than a decade, and here we synthesize these advances with outlooks for further progress.

    This review aims to summarize recent progress in studying how ENSO forces the Indo-TNW Pacific oceans and how this response develops and persists to exert climatic influences. The rest of the paper is organized as follows: Section 2 introduces post-ENSO anomalies in the ocean and atmosphere. It addresses questions of what are the major anomalies and how they are related to each other. Historical perspectives are provided of how progress has been made. Section 3 presents the coupled view and discusses the evidence. Section 4 explores the extent to which IO-TNW Pacific climate is predictable and highlights the challenges facing extratropical East Asian countries in developing skillful seasonal forecasts. Section 5 examines interdecadal variations in post-ENSO summer anomalies, based on historical observations that go back to the late 19th century. Section 6 is a summary with a conceptual model. It also discusses challenges in simulating Indo-Northwest Pacific climate and projecting its change in the face of increasing greenhouse gas forcing.

    Figure 2.  Lagged correlations with ND(0)J(1) Niño3.4 SST: (a) SST in the Niño3.4 region (black), North IO (5$^\circ$-25$^\circ$N, 40$^\circ$-100$^\circ$E; red), and TNW Pacific under the easterly trade wind regime (10$^\circ$-20$^\circ$N, 150$^\circ$-170$^\circ$E; blue); (b) SLP (purple) and precipitation (green) over the TNW Pacific around Guam (10$^\circ$-20$^\circ$N, 135$^\circ$-155$^\circ$E) [thick curves indicate the $>$95% confidence level, based on the $t$-test; three-month running averaging has been applied; based on ERSST, Hadley Centre sea level pressure, version 2 (Allan and Ansell, 2006) and CMAP for 1979-2014 (detrended)].

2. Ocean-atmosphere anomalies inpost-ENSO summer
  • This section highlights major anomalies over the summer tropical IO-TNW Pacific, with an historical account of how research has developed in the area, and a discussion of attendant anomalies in the extratropical East Asia.

    Figure 3.  Schematic representation of the major SST anomalies and atmospheric teleconnection over the Indo-Pacific oceans associated with El Niño events: (a) El Niño impacts on the South IO through westward Rossby waves during December-February; (b) Rossby waves inducing Southwest IO warming, which in turn induces an anti-symmetrical wind pattern over the tropical IO during March-May; (c) the second IO warming exciting a tropospheric Kelvin wave propagating into the western Pacific, forcing the AAC and PJ/EAP pattern to affect East Asia during the following summer.

  • Using EOF analysis, (Weare, 1979) showed that positive IO SST anomalies are often associated with a warmer eastern tropical Pacific, even though observations were quite sparse in those early days (Kent et al., 2007). Accompanying the SST mode are coherent anomalies of rainfall and SLP over the Arabian Sea (Weare, 1979). The maximum warming of the IO occurs from March to May, lagging the peak of SST anomalies over the eastern Pacific by about 3 months (Nigam and Shen, 1993). Traditionally, the IO warming is considered basin-wide (Liu and Alexander, 2007; Schott et al., 2009) and due to surface heat flux changes induced by El Niño via an atmospheric bridge (Klein et al., 1999; Alexander et al., 2002). Recent studies have revealed that the IO warming is mechanistically distinct among sub-basins.

    The early study of (Klein et al., 1999) pointed out that surface flux anomalies cannot explain the warming in the Southwest IO. Atmospheric models coupled to a motionless mixed layer ocean, forced by observed SST over the tropical Pacific, underestimate the Southwest IO warming (Alexander et al., 2002; Lau and Nath, 2003). There is growing consensus that Southwest IO SST variability is caused by thermocline displacements forced by ENSO through an atmospheric bridge (Xie et al., 2002; Du et al., 2009). During the developing (September-November) and mature (December-February) phases of El Niño, an anomalous anticyclone forms in the Southeast IO (Fig. 3a; Wang et al., 2000), associated with a weakened Walker circulation. In the South IO, the AAC forces downwelling ocean Rossby waves that propagate westward (Fig. 3b; Perigaud and Delecluse, 1993; Masumoto and Meyers, 1998; Ueda and Matsumoto, 2000). The Southwest IO is unique where the meridional shear of the trade winds maintains a thermocline ridge where thermocline feedback on SST is strong (Xie et al., 2002). The El Niño-induced downwelling Rossby waves deepen the thermocline, causing the Southwest IO to warm (Fig. 3b). The slow-propagating ocean Rossby waves anchor the Southwest IO warming, allowing it to persist through the following summer.

    The Southwest IO warming anchors an asymmetrical pattern of anomalous atmospheric circulation over the tropical IO in the spring following El Niño, with the northeasterlies north and northwesterlies south of the equator (Figs. 3c and 4). The anti-symmetrical atmospheric pattern can be explained by the WES feedback of (Xie and Philander, 1994). During winter and the following spring, the Southwest IO warming induces wind anomalies across the equator, and the wind anomalies turn northeasterly over the North IO due to the Coriolis effect. The anomalous northeasterlies over the North IO intensify the climatological northeast winter monsoon and cool the sea surface (Kawamura et al., 2001; Wu et al., 2008). The anti-symmetrical pattern is also obvious in precipitation. The rainfall increases over the anomalously warm South IO with enhanced convection and decreases over the relatively cool North IO. With the wind reversal to the southwest monsoon in May, the anomalous northeasterly winds change to have a warming effect on the North IO by reducing latent heat flux (Du et al., 2009; Fig. 4). Although wind-induced latent heat flux is the mechanism, the second warming of the North Indian Ocean in the early summer following El Niño results from ocean-atmosphere interaction within the tropical IO as the anti-symmetric wind pattern is anchored by the slow-propagating downwelling Rossby waves south of the equator. This deviates from the previous paradigm that the tropical IO is climatically dormant and can be modeled as a motionless mixed layer. Section 3 shows that the ocean-atmosphere interaction for the second warming of the North IO and SCS extends beyond the IO and involves the TNW Pacific.

    The largest SST anomalies in post-El Niño summer take place over the SCS because of ocean dynamic effects such as upwelling and gyre adjustments (Wang et al., 2002; Xie et al., 2003; Wang et al., 2006). The slow ocean dynamic adjustments also make SCS SST anomalies last longest of the global ocean (Yang et al., 2015). The shortwave cloud radiative effect also contributes to SCS SST variability (Klein et al., 1999; Wu et al., 2014).

  • The success of the thermally forced atmospheric Rossby wave theory of (Hoskins and Karoly, 1981) in explaining the observed excitation of the PNA pattern in winter by ENSO (Horel and Wallace, 1981) triggered a boom of research on tropical-extratropical teleconnections. From a teleconnectivity map based on six summers of monthly satellite cloud data, (Nitta, 1986) discovered a meridional dipole pattern of cloudiness between the tropical (15°-25°N) and midlatitude (30°-40°N) Northwest Pacific: weaker-than-normal convective activity over the South China and Philippine seas is associated with an increase in Mei-yu frontal rainfall (Fig. 5b). (Nitta, 1987) named this teleconnection the PJ pattern [also known as the East Asia-Pacific (EAP) pattern, as per (Huang and Sun, 1992)]. Figure 5 shows the PJ pattern extracted as the leading EOF of 850 hPa zonal wind over the summer Northwest Pacific multiplied by the Coriolis parameter, equivalent to the meridional pressure gradient. It is highly correlated with the principal components of the leading EOF modes of precipitation and lower-tropospheric vorticity in the region. Anomalous circulation in the lower troposphere exhibits a tripolar pattern (Fig. 5a). The PJ pattern refers to the dipole between the tropical and midlatitude lobes (association of the tropical and high-latitude lobes is weak). The PJ pattern dominates on intraseasonal to interannual time scales and affects summer temperature, precipitation, and TC landfall in East and Southeast Asia.

    Figure 4.  Time-latitude section of regression upon ND(0)J(1) Ni\ n3.4 SST: SST (shaded; $^\circ$C) and surface wind velocity (vectors), zonally averaged in the tropical IO (40$^\circ$-100$^\circ$E) [zonal wind climatology plotted in black contours (2 m s$^-1$ intervals with zero omitted)]. Reprinted from Du et al. (2009).

    Figure 5.  Structure of the PJ pattern. Anomalies of (a) SLP, (b) precipitation, (c) 2 m air temperature, and (d) TC occurrence regressed against the leading principal component of JJA seasonal-mean zonal wind velocity at 850 hPa multiplied by the Coriolis parameter over (10$^\circ$-55$^\circ$N, 100$^\circ$-160$^\circ$E) for 1979-2014 (detrended), based on JRA-55. The mode explains 35% of the variance. Panels (a, c) are based on JRA-55, and (b) is based on CMAP. For (d), TC occurrence is defined as the duration for which TCs are centered within 500 km from each grid point in a season, based on the best track data of the Regional Specialized Meteorological Center Tokyo-Typhoon Center. TCs and TC-originated extratropical cyclones with maximum wind speed exceeding 17.2 \mboxm s$^-1$ are examined. Stippling indicates the $>$95% confidence level, based on the $t$-test.

    2.2.1. Atmospheric dynamics

    Analogous to the winter PNA pattern, (Nitta, 1987), (Kurihara and Tsuyuki, 1987) and (Huang and Sun, 1992) suggested that the PJ pattern is a Rossby wave train excited by anomalous convection over the TNW Pacific. (Nitta, 1987) further speculated that the convection anomalies are forced by local SST anomalies. The PJ pattern has withstood the test of time but the excitation mechanism turns out to differ from what these early studies suggested.

    An alternative view to linear Rossby waves riding on the zonal mean flow regards dominant teleconnection patterns such as the PNA as barotropically unstable modes that gain energy from the zonally varying background flow (Simmons et al., 1983). From this viewpoint, the PNA pattern is an internal dynamical mode of the atmosphere while external forcing such as ENSO modulates its probability. Along this line, (Tsuyuki and Kurihara, 1989) suggested that over the midlatitude Northwest Pacific in summer, a barotropically unstable mode and Rossby wave propagation from the tropics constitute the PJ pattern. A problem was that the prevailing winds in the upper troposphere over the summer Northwest Pacific are northeasterly, preventing stationary Rossby waves from propagating poleward. Poleward Rossby-wave dispersion is, however, possible in the lower troposphere (Kosaka and Nakamura, 2006). (Kosaka and Nakamura, 2010) and (Hirota and Takahashi, 2012) suggested that the PJ pattern is an internal regional mode of the atmosphere, fueled by tropical convective variability and gaining energy also from the background state via barotropic and baroclinic energy conversion. The anomalous circulation feeds back to tropical convective anomalies by dynamically inducing vertical motion. In the midlatitudes, there is a similar feedback between latent heating and the PJ circulation: local latent heating is both a cause of circulation formation (Lu and Lin, 2009; Sun et al., 2010) and a result of the anomalous circulation through horizontal temperature advection (Kosaka et al., 2011). A variety of external perturbations, both in and out of the tropics, can trigger the PJ pattern (Arai and Kimoto, 2008; Hirota and Takahashi, 2012).

    2.2.2. SST forcing

    The local correlation between SST and precipitation anomalies of the PJ pattern is weak over the TNW Pacific (Wang et al., 2005; Wu et al., 2009a; Lu and Lu, 2014) and even negative over the SCS (Fig. 5), challenging Nitta's hypothesis of local SST forcing. The PJ pattern is not significantly correlated with the concurrent ENSO index (Kosaka and Nakamura, 2006), but with ENSO in the preceding winter (Fig. 6; Wang et al., 2003). The impact of ENSO on the summer East Asian monsoon in ENSO decay years has been related to the PJ pattern (Huang et al., 2004). The tropical lobe of the PJ pattern in post-El Niño summer is the AAC with suppressed convection over the TNW Pacific (Fig. 5). The latter is often called the Philippine Sea AAC (Wang et al., 2000, 2003), but we note that it extends into the North IO with easterly wind anomalies on the south flank (Fig. 7a), enabling inter-basin interactions between the IO and Northwest Pacific. The western extent of the AAC reaches the Bay of Bengal and India, and northeasterly anomalies over the Arabian Sea appear to be part of the anti-symmetric pattern across the equator tied to the Southwest IO warming induced by the downwelling ocean Rossby wave (section 2.1). Regarding the oceanic anchor for the AAC, there are two hypotheses pointing to SST anomalies of the TNW Pacific and tropical IO, respectively.

    Figure 6.  Lag correlations of the summer PJ index (leading principal component for Fig. 5) with Niño3.4 (solid) and tropical IO (20$^\circ$S-20$^\circ$N, 40$^\circ$-100$^\circ$E; dashed) SST (detrended; three-month running averaged). Thick curves represent the $>$95% confidence level, based on the $t$-test.

    Figure 7.  JJA anomalies of (a) SST (shading), surface wind velocity (arrows), (b) precipitation (shading) and normalized tropospheric (850-250 hPa mean) temperature (contours with an interval of 0.1; contours within $\pm$0.3 are omitted) regressed against Niño 3.4 SST in the preceding NDJ for 1978/79-2009/10 [based on JRA-55 (surface wind and tropospheric temperature), CMAP, and ERSST.v3b (Smith et al. 2008); 8-year high-pass filter has been applied beforehand; stippling indicates the $>$95% confidence level, based on the $t$-test, for shaded anomalies; red (blue) arrows indicate where the wind anomalies strengthen (weaken) climatological winds by more than 0.1 m s$^-1$].

    In boreal winter of an El Niño event, an AAC develops rapidly east of the Philippines (Fig. 2b; Zhang et al., 1996) and is coupled with local SST (Wang et al., 1999, 2000). The AAC cools the ocean on the southeastern flank by strengthening the prevailing northeast trade winds. The ocean cooling suppresses atmospheric convection, reinforcing the AAC with a Rossby wave response. Alternatively, Stuecker et al. (2013, 2015) suggested that nonlinear interactions of atmospheric response to slowly evolving SST anomalies of the eastern tropical Pacific with the background annual cycle dominate and cause the rapid growth of the TNW Pacific AAC. This nonlinear mechanism explains the mysterious biennial tendency of atmospheric variability over the TNW Pacific (Li and Wang, 2005), e.g., the rapid transition from negative JJA(0) to positive JJA(1) anomalies of atmospheric pressure (Fig. 2b). This so-called combination mode effect is weak in post-ENSO summer when eastern Pacific SST anomalies have dissipated (M. Stuecker et al., 2015, personal communication).

    The TNW Pacific air-sea coupling helps the AAC to persist but requires background northeasterly winds for positive feedback. In summer, the trade winds retreat eastward over the TNW Pacific (Fig. 1), limiting negative SST anomalies and the local air-sea feedback to a narrow region east of 140°E (Fig. 7a). (Wang et al., 2003) suggested that the local coupling can help the AAC to persist from winter to summer. Difficulties extending this hypothesis to summer include the weakening and contraction of the negative SST anomalies (Fig. 2a) associated with the eastward retreat of the easterly trade wind regime, reducing the relative importance of air-sea interaction in the easterly regime (Wu et al., 2010).

    The second hypothesis, called the IO capacitor effect, considers the IO memory of ENSO influence. Recognizing that the El Niño-induced IO warming persists through summer (Fig. 2), (Yang et al., 2007) suggested that it anchors the TNW Pacific AAC like a discharging capacitor. (Xie et al., 2009) proposed a discharging mechanism for this IO capacitor. The IO warming excites a Matsuno-Gill-type response in tropospheric temperature, with a Kelvin wave wedge penetrating into the equatorial western Pacific (Fig. 7b). The warm equatorial Kelvin wave is accompanied by surface Ekman convergence on, and divergence off, the equator, thereby suppressing convection over the TNW Pacific (Fig. 7a). (Terao and Kubota, 2005) considered a similar mechanism but emphasized the inter-basin gradient between the IO warming and a developing La Niña in the equatorial Pacific (Yun et al., 2013). An apparent paradox is that the couplet of AAC and suppressed convection in the western Pacific is found only on the northern flank of the tropospheric Kelvin wave, although the Kelvin wave itself is symmetric about the equator (Fig. 7). This interhemispheric asymmetry arises because convection is stronger in the summer than winter hemisphere, and a strong convective feedback preferentially amplifies the Kelvin wave perturbations in the summer NH (Xie et al., 2009).

    AGCM experiments show that the IO warming and TNW Pacific cooling contribute cooperatively to the summer TNW Pacific AAC (Ohba and Ueda, 2006; Wu et al., 2014). (Wu et al., 2010) found that the AAC is mainly due to local air-sea interaction in early summer but the IO effect dominates in the mid to late summer. A caveat is that AGCMs tend to exaggerate the local SST effect by simulating a positive local SST-precipitation relationship over the TNW Pacific, while the correlation is insignificant in observations (Wang et al., 2005; Wu and Kirtman, 2007). In a CGCM experiment, suppressing tropical IO SST variability reduced the intensity of the summer TNW Pacific AAC by roughly 50% (Chowdary et al., 2011). It remains to be investigated what accounts for the other 50% of the AAC intensity——a question to be revisited in section 3. Therein, we propose a unifying view that combines the local air-sea interaction hypothesis of (Wang et al., 2003) and the IO capacitor of (Xie et al., 2009).

    Statistically, eastern tropical Pacific SST anomalies diminish in JJA(1) (Fig. 2a) but individual ENSO events differ among themselves during the decay. For example, a strong La Niña event developed in 1998 summer (with Niño3.4 SST at -1.2°C) following a record El Niño. Such variability in the SST gradient between the IO and tropical Pacific contributes to the TNW Pacific AAC (Terao and Kubota, 2005; Chen et al., 2012; Cao et al., 2013; Xiang et al., 2013). Recent studies have also suggested a contribution from the tropical Atlantic (Rong et al., 2010; Hong et al., 2014; Chen et al., 2015; Yu et al., 2015). All these——IO warming, the TNW Pacific AAC, tropical Pacific cooling, and tropical Atlantic warming——may not be mutually independent (Kug and Kang, 2006; Stuecker et al., 2015; Li et al., 2015c), highlighting the need for a generalized view of inter-basin interactions.

  • 2.3.1 Northwest Pacific TCs and Indian rainfall

    Coherent anomalies of summer TC activity over the Northwest Pacific accompany the PJ pattern (Fig. 5d; Choi et al., 2010; Kim et al., 2012). In post-El Niño summer, the AAC is unfavorable for TC development. TC genesis decreases over most of the TNW Pacific while slightly increasing over the SCS, consistent with the pattern of vertical wind shear change (Du et al., 2011). TC occurrences drop in a region centered on Okinawa, with significantly reduced landfall on the coasts of eastern China and Korea (Fig. 5d; Wang et al., 2013). These TC anomalies are captured in high-resolution AGCM simulations, pointing to the importance of SST boundary conditions (Mei et al., 2015). Using a regional atmospheric model, (Zhan et al., 2011) showed that eastern IO SST anomalies affect TC genesis over the TNW Pacific by modulating the western Pacific summer monsoon via the equatorial Kelvin wave.

    The TNW Pacific AAC extends into the North IO, affecting South Asia (Mishra et al., 2012). In post-El Niño summer, most of the South Asian region receives normal to above-normal rainfall despite weak monsoon winds (Park et al., 2010; Chowdary et al., 2013). The anomalous warm SST promotes evaporation and increases atmospheric moisture over the North IO (e.g., Saha, 1970). Enhanced moisture transport (Izumo et al., 2008) and moist stability increase rainfall in the Western Ghats and southern peninsular of India (Yang et al., 2007; Park et al., 2010), while the westward extension of the TNW Pacific AAC acts to reduce rainfall over the eastern Indo-Gangetic Plain (Chowdary et al., 2013).

    Figure 8.  Air-sea coupling of the IPOC mode in a 200-year partial coupling experiment called NoENSO, which artificially suppresses SST variability over the tropical eastern Pacific: (a, b) anomalies of (a) SST (shading), normalized tropospheric temperature (contours for $\pm$0.05, $\pm$0.15, $\pm$0.25, \ldots$^\circ$C), (b) precipitation (shading) and surface wind (arrows) regressed against the leading principal component of monthly 850 hPa vorticity over (0$^\circ$-60$^\circ$N, 100$^\circ$-160$^\circ$E) for JJA (stippling indicates the $>$95% confidence level of shaded fields, based on the $t$-test); (c) lag cross-correlation of the corresponding principal component with SST in the northern IO (0$^\circ$-25$^\circ$N, 60$^\circ$-120$^\circ$E; red) and TNW Pacific easterly regime (10$^\circ$-20$^\circ$N, 150$^\circ$-170$^\circ$E; blue) [error bars represent the 95% confidence intervals; based on Kosaka et al. (2013) with slight model updates].

    2.3.2. Summer variability over East Asia

    The PJ pattern provides a pathway for tropical influences on the East Asian summer monsoon. In the polarity shown in Fig. 5 (corresponding to a post-El Niño summer), the PJ pattern brings anomalously wet and cool conditions to the Yangtze River valley, Korea, and Japan. It prevents the seasonal northward migration of the Northwest Pacific subtropical high and Mei-yu rainband, resulting in a prolonged rainy season with reduced sunshine in these regions. The mega El Niño of 1997/98 caused the great Yangtze River flood in 1998 through the PJ pattern (Chowdary et al., 2011).

    (Huang and Wu, 1989) suggested that summer rainfall anomalies in East Asia depend on the phase of the ENSO cycle, relating the differences between the ENSO developing and decay summers to tropical convection over the South China and Philippine seas. Subsequent studies (Shen and Lau, 1995; Chang et al., 2000; Wang et al., 2000; Wu et al., 2003) showed that in post-El Niño summer the TNW Pacific AAC causes above-normal rainfall in the Yangtze River valley. The relationship between East Asian summer rainfall and ENSO is unstable over time (Wu and Wang, 2002; Ye and Lu, 2011), possibly due to the slow modulations by variations in ENSO amplitude and/or type (Xie et al., 2010; Feng et al., 2011; Yuan and Yang, 2012; Li et al., 2014). Further complications include apparent asymmetry between polarities in the leading mode of East Asian summer rainfall variability (Hsu and Lin, 2007).

    In post-El Niño summer, anomalous vertical motions associated with the PJ pattern cause positive surface temperature anomalies in southern China and negative anomalies in northeast China by changing shortwave radiation and adiabatic warming (Hu et al., 2011). The circulation anomalies also cause more frequent heat waves than normal across the southern Yangtze River Valley in late summer (Hu et al., 2012). In Japan, the PJ pattern is one of dominant modes for summer temperature (Fig. 5c; Wakabayashi and Kawamura, 2004; Yasunaka and Hanawa, 2006), contributing to heat waves (e.g., in 2004) and extreme cool summers (e.g., in 1993). The record cool and wet summer of 1993 caused a major rice harvest failure in Japan, pushing the nation to open its domestic rice market.

3. A coupled perspective
  • In post-El Niño summer, the warming of the North IO and SCS causes the AAC via the warm tropospheric Kelvin wave (section 2.2), while anomalous easterly winds on the southern flank of the AAC cause the second warming of the North IO and SCS. The circular argument indicates that the two are a coupled phenomenon. (Kosaka et al., 2013) identified such a coupled mode that involves inter-basin interaction between the North IO and TNW Pacific, using the Pacific Ocean-Global Atmosphere partial coupling framework, where SST variability in the tropical Pacific is strongly damped towards zero ("NoENSO" experiment).

    Figure 9.  Seasonal evolution of the IPOC mode in the 200-year NoENSO run: (a) SST (shading), precipitation (contours for $\pm$0.2, $\pm$0.4, $\pm$0.6, $\ldots$ mm d$^-1$) and 10 m wind (arrows) anomalies averaged over 10$^\circ$-20$^\circ$N regressed against the leading principal component of JJA seasonal-mean 850 hPa vorticity over (0$^\circ$-60$^\circ$N, 100$^\circ$-160$^\circ$E) (red and blue arrows indicate that the corresponding wind speed anomalies are greater than 0.1 and less than $-0.1$ m s$^-1$, respectively; stippling indicates the $>$95% confidence level for SST anomalies, based on the $t$-test); (b) climatological 10 m wind velocity (arrows) and its zonal component (shading with zero contour; three-month sliding average applied).

    Even without ENSO, the PJ pattern is coupled with positive SST anomalies over the North IO and SCS, along weak negative anomalies in the easterly regime of the TNW Pacific (Fig. 8a). Negative precipitation anomalies peak on the boundary between positive and negative SST anomalies in the westerly and easterly regimes of the TNW Pacific, respectively. The anomalous diabatic cooling over the TNW Pacific forces an AAC as a cold atmospheric Rossby wave that propagates into the North IO. The associated easterly anomalies on the southern flank (Fig. 8b) weaken the monsoon westerlies and reduce surface evaporation, causing the North IO and SCS to warm. The ocean feedback to the AAC is non-local, as the spatial correlation between SST and precipitation anomalies is weak (Fig. 8). By forcing tropospheric temperature to follow a moist adiabatic profile in the vertical direction (Neelin and Su, 2005), the North IO warming then excites a warm atmospheric Kelvin wave (Fig. 8a), suppressing convection and energizing the AAC over the TNW Pacific. The inter-basin air-sea interaction supports positive feedback between the North IO warming and AAC. Indeed, the cross-correlation between the PJ pattern and North IO SST peaks at zero lag (Fig. 8c), indicating positive feedback. As another manifestation of the ocean-atmosphere feedback, both the magnitude and temporal persistence of PJ variability substantially increases in the coupled relative to the atmospheric experiment (Kosaka et al., 2013).

    (Kosaka et al., 2013) focused on the IO-PJ coupling and suggested the prevailing monsoon westerlies as the necessary condition. Here, we extend their analysis to examine the pre-season evolution. Note that equatorial Pacific SST anomalies are kept near zero all the time in the NoENSO experiment. The JJA IO-PJ coupling is preceded by negative anomalies of SST and precipitation over the TNW Pacific (Fig. 9a). In the pre-season (April-May) TNW Pacific, negative SST anomalies are collocated with northeasterly wind anomalies on the southeastern flank of an AAC that extends into the North IO (Fig. 10a). The interaction of negative SST anomalies and the AAC under the northeast trades over the spring TNW Pacific constitutes positive feedback, as envisioned by (Wang et al., 2000). The seasonal variation in the background wind over the TNW Pacific alters the type of feedback that prevails in different seasons. The monsoon westerly regime appears in the North IO in May and expands eastward through the SCS into the TNW Pacific (Fig. 9b). The eastward seasonal expansion of the monsoon westerlies leaves a clear signature in the boundary between the expanding positive and contracting negative SST anomalies in the coupled IO-TNW Pacific mode (Fig. 9a). The easterly anomalies of the AAC induce negative SST anomalies under the easterly trades but create positive anomalies under the monsoon westerlies (Fig. 10b). This seasonally evolving coupled mode unifies the local air-sea interaction mechanism of (Wang et al., 2000) that dominates in spring under the northeast trades over the TNW Pacific, and the IO capacitor effect of (Xie et al., 2009) that takes over in summer under the southwest monsoon.

    Figure 10.  As in Fig. 9a but horizontal maps for (a) preceding April-May and (b) concurrent July-August [precipitation anomalies are omitted for clarity; red (blue) arrows indicate where the wind anomalies strengthen (weaken) climatological winds].

    Figure 11.  Composited anomalies for JJA in 1983, 1992 and 1998 (summers following major El Niño events) based on (a, b) observations and (c, d) the multi-model ensemble mean of seasonal predictions by 11 coupled models initialized on 1 May: (a, c) SST (shaded; $^\circ$C), SLP (contours; every 0.5 hPa), 850 hPa wind (vectors; magnitudes above 0.3 m s$^-1$ are displayed); (b, d) precipitation (shaded; mm d$^-1$) and tropospheric temperature represented by 200-850 hPa thickness (contours; gpm). Reprinted from Chowdary et al. (2010).

    Figure 12.  JJA(1) differences in (a) SST (shaded; $^\circ$C) and 850 hPa wind anomalies (arrows; magnitudes exceeding 0.3 m s$^-1$ are displayed) and (b) precipitation (shaded; mm d$^-1$) and SLP (contours; hPa), between CTL and NoTIO predictions with a 1-month lead (initialized on 1 May) by the CGCM of Luo et al. (2008), based on the composites of three El Niño decay years (1983, 1992 and 1998).

    This Indo-western Pacific inter-basin coupling itself does not require ENSO forcing, but El Niño excites this mode by inducing the IO warming (Kosaka et al., 2013) and TNW Pacific cooling (Wang et al., 2013; Stuecker et al., 2015) as initial perturbations. This coupled mode generalizes the capacitor concept and constitutes an Indo-western Pacific ocean capacitor (IPOC). In the peak phase of ENSO, the tropical Pacific is the center of action featuring, globally, the most pronounced anomalies of SST, precipitation, and surface wind. By contrast, in JJA(1), the discharging IPOC shifts the ENSO's center of action to the Indo-TNW Pacific region, where the most pronounced and coherent anomalies are found. The positive feedback among the TNW Pacific cooling, North IO warming and AAC prolongs ENSO anomalies and explains why the decay of El Niño follows the spatiotemporal pattern of the IPOC mode, both in JJA(1) (Fig. 7) and the pre-season (Fig. 10a). Thus, the IO "basin mode" (Yang et al., 2007) is truly a dynamic mode, as the inter-basin interaction sustains it against dissipation. While observations suggest cross-basin ocean-atmosphere interaction (Du et al., 2009; Wang et al., 2013), the NoENSO partial coupling experiment of (Kosaka et al., 2013) shows that IPOC is an intrinsic mode of the region with a distinctive seasonal evolution dictated by monsoon. The PJ pattern is an atmospheric internal mode (Lu et al., 2006) but energized by ocean coupling and ENSO forcing. The seasonally varying IPOC brings seasonal predictability to the region (section 4). The mode also emerges from the inter-member spread of ensemble seasonal predictions (Li et al., 2012) as differences in initial conditions grow on the IPOC feedback.

4. Predictability
  • CGCMs, properly initialized with observations, show skill in predicting precipitation and circulation anomalies over the TNW Pacific during summer following El Niño at monthly to seasonal leads (Liang et al., 2009; Wang et al., 2009; Chowdary et al., 2010; Lee et al., 2011). Figure 11 compares 11-model mean forecasts with observations in composites of three post-El Niño summers with a significant IO warming (in 1983, 1992 and 1998). At one month lead (initialized on 1 May), the multi-model ensemble captures the salient features of the IPOC mode, i.e., the collocated anomalies of SST increase and weakened monsoon winds over the North IO and SCS, the warm tropospheric Kelvin wave wedge into the western Pacific, as well as the AAC that extends from the TNW Pacific into the North IO. Models have good skill in predicting summer monsoon rainfall over the Indo-TNW Pacific, as well as South and East Asia (Fig. 11d). At three-month (initialized on 1 March) lead, significant skill remains in predicting the AAC and rainfall anomalies over the TNW Pacific (Chowdary et al., 2010; Li et al., 2012, Lu et al., 2012; Jiang et al., 2013).

    Figure 13.  Structure of the Silk Road pattern: 200 hPa geopotential height anomalies (shading) regressed against the (a) leading and (b) second principal components of JJA-mean 200 hPa meridional wind velocity over (30$^\circ$-50$^\circ$N, 30$^\circ$-130$^\circ$E), which explain 40.2% and 20.7% of variance, respectively (stippling represents the $>$95% confidence level, based on the $t$-test; grey contours indicate JJA climatological zonal wind velocity at 200 hPa for 20, 25 and 30 m s$^-1$; based on JRA-55 for 1979-2014) (detrended).

    The IO effect on the prediction is studied with a "NoTIO" experiment, where climatological SST is prescribed over the tropical IO. Figure 12 shows the JJA(1) composite difference in circulation, precipitation and SLP between control (CTL) and NoTIO runs in one-month lead forecasts. Seasonal anomalies are strengthened by IO SST variability. Specifically, the IO warming increases local precipitation and induces an AAC with reduced precipitation over the TNW Pacific. The CTL-NoTIO differences clearly illustrate the importance of tropical IO air-sea interaction in predicting circulation and rainfall over the Indo-TNW Pacific region. An interactive tropical IO extends the useful anomaly correlation coefficient (r>0.5) in predictions of circulation anomalies over the TNW Pacific by 1-2 months (Chowdary et al., 2011).

  • To the extent that atmospheric circulation and rainfall anomalies are predictable over the IO-TNW Pacific, the PJ pattern allows these tropical anomalies to influence the midlatitude East Asian and Northwest Pacific region and conceivably enhances predictability there. Indeed, prediction studies show some skill, i.e., increased rainfall and southwesterly wind anomalies over eastern China and the south of Japan in post-El Niño summer (Fig. 11). Generally, however, the predictability in East Asia is limited, both due to model errors in simulating the Mei-yu rain band and to pronounced internal variability of the atmosphere that is unpredictable at monthly and longer leads.

    For the summer of 2010, a multi-model ensemble predicted a PJ mode but the prediction was verified only in the tropics: Monsoon rainfall intensified over the Arabian Sea and weakened over the TNW Pacific, typical of a post-El Niño summer. Deviating from the dipolar PJ pattern, however, Korea and Japan experienced extreme hot weather while northwest Pakistan was devastated by heavy floods. These floods are attributed to unusual atmospheric events in the tropics, with deep convection shifted from the Bay of Bengal to northern Pakistan (Houze et al., 2011; Pai and Sreejith, 2011; Webster et al., 2011). Midlatitude circulation triggered by a blocking high that caused the Russian heat wave also contributed to the Pakistan heavy rains downstream (Lau and Kim, 2012; Kosaka et al., 2012). Models show some skill in predicting the distinct seasonal rainfall anomalies in summer 2010 from the northern Arabian Sea to northern Pakistan, but this predictability comes from the tropical region (Chowdary et al., 2014). Models failed to predict the extreme intensity of northern Pakistan rainfall and positive precipitation anomalies in western Pakistan due to the inadequate representation of subtropical circulation, such as the Silk Road pattern.

    The Silk Road pattern is the wavy component of the summer circumglobal teleconnection pattern in the Eurasian sector, trapped in the waveguide of the subtropical Asian jet (Fig. 13; Wu, 2002; Enomoto, 2004; Ding and Wang, 2005; Kosaka et al., 2009). In summer 2010, the Silk Road pattern caused an anomalous anticyclonic circulation over Japan and a cyclonic circulation over west-central Asia around 40°N. Coupled models can simulate the stationary wave pattern of the Silk Road teleconnection (anchored by zonal variations of the Asian jet) but not the temporal phase (Kosaka et al., 2012; Chowdary et al., 2014). This indicates that the Silk Road pattern is an internal mode of the midlatitude atmosphere, whereas the zonal-mean component of the summer circumglobal teleconnection pattern is correlated with developing ENSO (Ding et al., 2011) and hence is predictable (Lee et al., 2011, 2014). Because chaotic phase variations of the Silk Road pattern are not strongly tied to SST forcing, it limits the predictability at monthly and longer leads over East Asia even though the PJ pattern transmits predictable tropical influences. Some recent studies, however, suggest an association of the Silk Road pattern with Atlantic SST (Wu et al., 2009b; Yamaura and Tomita, 2011; Otomi et al., 2013). This is a potential source of predictability that can benefit midlatitude Asian countries.

    Figure 14.  (a) Lag correlation in a 21-year sliding window of North IO SST averaged along a shipping track with respect to ND(0)J(1) Niño3.4 SST (black contours represent the 95% confidence level and white contours represent correlations of 0.8). (b) 21-year sliding variance of ND(0)J(1) Niño3.4 SST (red) and D(0)JF(1) Southern Oscillation Index (SOI; scaled by 2.8; blue). (c) 21-year sliding correlation of the PJ index [difference of normalized station pressure records between Yokohama, Japan and Hengchun, Taiwan, in JJA; Kubota et al. (2015); purple] and North IO shipping track SST in JJA(1) with SOI in D(0)JF(1). Note that the PJ index is defined in the opposite polarity of the pattern shown in Figs. 3 and 5-12, and positive SOI corresponds to La Niña. Dashed horizontal lines indicate the 95% confidence level, based on the $t$-test. The year refers to the center of a given 21-year window. (a, b) Reprinted from Chowdary et al. (2012); (c) Reprinted from Kubota et al. (2015).

    Figure 15.  Schematic representation of cross-basin Indo-Pacific ocean-atmosphere interaction in JJA(1) following El Niño: anomalies of SST (color shading), surface wind (vectors), and SLP (shaded ellipses). The easterly wind anomalies associated with the AAC cause SST to increase over the North IO-SCS (blue vectors) and to decrease in the easterly regime of the Northwest Pacific (red vectors), while the SST anomalies anchor the AAC by suppressing atmospheric convection over the TNW Pacific. The slow propagating oceanic Rossby waves in the South IO (red wavy arrow) also contribute to the easterly wind anomalies over the North IO (box arrow). Convection is suppressed in the AAC but enhanced over East Asia in the anomalous cyclonic circulation (ACC) of the PJ pattern.

5. Interdecadal modulations
  • ENSO teleconnections to the IO-TNW Pacific and East Asia show substantial interdecadal variations over the second half of the 20th century, a period of relatively abundant observations. The relationship of the East Asian summer monsoon and TNW Pacific AAC to the preceding ENSO was strong after the late 1970s but insignificant from the 1950s to 1970s (Wu and Wang, 2002; Wang et al., 2008; Xie et al., 2010). Consistent with the IO capacitor mechanism, the El Niño-induced IO warming persists through summer only after the 1970s as the thermocline in the tropical Southwest IO shoaled to strengthen thermocline feedback (Xie et al., 2010). Tracking the tropospheric Kelvin wave that connects the IO warming and western Pacific, tropospheric temperature in long-term sounding observations over Singapore shows a corresponding increase in correlation with ENSO. An AGCM forced with observed SST successfully simulated the increase in the ENSO-AAC correlation and AAC variance throughout the 1970s (Huang et al., 2010). Using an AGCM coupled with an ocean mixed layer, (Ding et al., 2015) reproduced the interdecadal modulation in partial coupling experiments that restored SST towards observations over the equatorial Pacific.

    (Chowdary et al., 2012) used surface ocean-atmospheric observations along a busy shipping track across the North IO and SCS to extend the analysis back to 1871——the year of Suez Canal opening, which consolidated IO shipping lanes. The correlation between summer North IO SST and preceding winter ENSO was high at the turn of the 20th century and since the mid-1970s, but was low in between (Fig. 14a). The North IO SST modulations were accompanied by consistent modulations in local wind, as well as in remote pressure and rainfall over the TNW Pacific. (Kubota et al., 2015) used station data of atmospheric pressure to reconstruct the PJ pattern from 1897 and found similar modulations in correlation with the preceding winter ENSO, with significant correlations before the 1910s, around the 1930s, and since the 1970s (Fig. 14c). As similar modulations happened before, the recent increase in correlation between the IPOC mode and ENSO appears to be due to natural variability, rather than to anthropogenic climate change (Zheng et al., 2011). In support of this notion, interdecdal modulations of the ENSO effect on Indo-TNW Pacific summer climate are common in climate model simulations under constant radiative forcing (Hu et al., 2014). The interdecadal modulations indicate that the seasonal predictability of summer IO-WNP climate varies from one decade to another.

    ENSO amplitude can affect the strength of ENSO teleconnection to the Indo-TNW Pacific region. The period, amplitude, spatial structure, and temporal evolution of El Niño events can cause significant changes in ENSO teleconnections (Diaz et al., 2001). When ENSO variance is high (at the turn of the 20th century and after the 1970s) (Fig. 14b), correlations of atmospheric anomalies in the Indo-TNW Pacific with ENSO are high (Chowdary et al., 2012; Kubota et al., 2015; Yang et al., 2015). Variations in El Niño to La Niña transition and the persistence of IO warming may also affect the TNW Pacific AAC in summer (Xie et al., 2010). For example, the intensified ENSO-PJ correlation in the 1930s is not associated with an ENSO amplitude increase, but rather with an increase in IO warming persistence (Fig. 14d). The Pacific Decadal Oscillation is an additional factor that can modulate the ENSO impact on Indo-TNW Pacific climate (Wang et al., 2008; Feng et al., 2014).

    Figure 16.  Scatter diagrams (a) between zonal wind (m s$^-1$) and SST ($^\circ$C) anomalies in the North IO (0$^\circ$-15$^\circ$N, 50$^\circ$-100$^\circ$E) in AMJ(1) and (b) between the standard deviation of NDJ(0/1) Niño3.4 index [STD(Niño)] and the correlation of the JJA(1) tropical IO basin-mean SST [r(IOB, Niño)], based on historical runs with 20 CMIP5 models (error bars give ranges of one standard deviation). Reprinted from Du et al. (2013).

6. Summary and outlook
  • ENSO is a climate phenomenon that opens on the center stage of the equatorial Pacific. The last act of El Niño drama is played over the Indo-western Pacific in JJA(1) after the curtain falls on the main stage. The main cast of the last act includes the surface warming in the westerly monsoon regime of the Indo-western Pacific warm pool, and the AAC that extends from the TNW Pacific into the North IO. Here, we have reviewed recent advances, with a historical perspective, in the investigation of how the last act is staged.

    Our synthesis has revealed the IPOC mode sustained by inter-basin ocean-atmosphere interaction (Fig. 15). IPOC unifies two separate ideas for the post-El Niño summer AAC that emphasize either the sea surface cooling in the easterly trade regime of the TNW Pacific (Wang et al., 2000), or the sea surface warming in the westerly monsoon regime over the IO and SCS (Xie et al., 2009). The zonal contrast between the IO warming and Pacific cooling was previously recognized (Terao and Kubota, 2005; Ohba and Ueda, 2006) as important for the AAC, but the discussion was limited to an atmospheric, not coupled, perspective. The coupled perspective further recognizes that the North IO warming and TNW Pacific cooling are caused by the easterly wind anomalies on the southern flank of the AAC that weaken the westerly monsoon and strengthen the easterly trade winds (Du et al., 2009). The interaction of the SST anomalies and AAC yields positive feedback.

    The IPOC is an internal mode arising from inter-basin ocean-atmosphere feedback, as illustrated by the NoENSO partial coupling experiment of (Kosaka et al., 2013). In mid-summer, IO SST anomalies are the major cause of the AAC (Wu et al., 2010) as the easterly trade regime retreats eastward over the TNW Pacific, reducing the area of the SST cooling. The free IPOC mode shows a seasonal evolution preceded by the TNW Pacific cooling-AAC coupling in spring. Remarkably, the TNW Pacific cooling-AAC coupling in the free mode happens to resemble what is observed during the El Niño decay in spring (Wang et al., 2000, 2003). This indicates that ENSO preferentially excites the IPOC mode because of the reduced damping. In addition to the TNW Pacific cooling, the El Niño-induced downwelling Rossby waves in the South IO also help initialize the IPOC mode by anchoring a meridional anti-symmetric wind pattern with anomalous easterlies over the Arabian Sea (Fig. 15; Du et al., 2009). The easterly wind anomalies, induced by the ocean Rossby waves, and as part of the AAC, cause the second warming of the North IO and SCS upon the onset of the westerly monsoon. The second warming manifests the unstable interaction of the North IO and AAC.

    An atmospheric bridge allows ENSO to imprint upon the SST in other ocean basins (Lau and Nath, 1996; Alexander et al., 2002). The IO capacitor emphasizes that IO SST anomalies induced by the atmospheric bridge outlast ENSO forcing itself and discharge regional climatic influences (Yang et al., 2007; Xie et al., 2009). Our work here extends the ocean capacitor concept by revealing the coupled ocean-atmosphere feedback beyond a simple persistence due to ocean thermal inertia. The positive feedback of IPOC explains why El Niño stages its last act over the Indo-Northwest Pacific region in JJA(1), why the North IO-SCS warming peaks twice, and why the AAC is the dominant mode of summer atmospheric variability over the Northwest Pacific. These results, along with the recognition that the IOD is a coupled mode of Bjerknes feedback excited by ENSO (Saji et al., 1999), transform our view of the IO from a slave to ENSO to a dynamic player shaping regional climate variability (Annamalai et al., 2005; Kug and Kang, 2006; Luo et al., 2012; Han et al., 2014; Li et al., 2015c).

    Models show skill in predicting the IPOC mode at monthly to seasonal leads, especially after a major El Niño event (Wang et al., 2009; Chowdary et al., 2010). Although the PJ pattern transmits tropical signals poleward, seasonal predictability is limited over extratropical East Asia due to the interference by stationary wave trains trapped along the Asian westerly jet (Kosaka et al., 2012). Models simulate these stationary wave patterns well, but not their temporal phase. Further work is needed to quantify seasonal predictability over East Asia, including the contribution from the PJ pattern and limitations imposed by the Silk Road pattern. Extra predictability might be achieved by improving the simulation of the Mei-yu rain band in light of the importance of midlatitude latent heating for the PJ pattern (Lu and Lin, 2009). Prediction systems with a high-resolution (50 km or finer grid spacing) atmospheric model component hold the promise of predicting TC track density and even landfall probability at seasonal leads (Vecchi et al., 2014; Mei et al., 2015).

    Historical correlations of summer anomalies over the Indo-TNW Pacific with the preceding winter ENSO were not stable over time——high at the turn of the 20th century and after the 1970s, but low in between. The ENSO variance cycle seems to be a driver: strong ENSO excites a robust IPOC mode with enhanced PJ variance (Chowdary et al., 2012; Kubota et al., 2015). Bursts of strong ENSO events tend to cluster in time to form a variance cycle (Li et al., 2013). Because it affects the seasonal predictability, work is needed to investigate the mechanism for the ENSO variance cycle and its modulations of teleconnective effects (Ogata et al., 2013; Wittenberg et al., 2014).

    CGCMs are an important tool for seasonal prediction and future projection. Many CGCMs show skill in simulating the El Niño-induced IO warming (Saji et al., 2006), its seasonal evolution, and the underlying mechanisms (e.g., ocean Rossby waves in the South IO) (Du et al., 2013). Consistent with the IPOC mechanism, the SST warming and easterly wind anomalies in early summer of the El Niño decay year are correlated in the inter-model spread of CMIP5, and ENSO variance modulates the magnitude of the post-El Niño IO warming (Fig. 16). A common bias of CMIP5 models is that the El Niño-induced IO warming and AAC terminate 1-2 months too early and do not persist through summer as in observations (Du et al., 2013; Hu et al., 2014). This bias of weak summer persistence might be due to a weak thermocline feedback of slow-propagating Rossby waves over the southwest IO——a mechanism that contributes to the persistence of the IPOC mode (Du et al., 2009). The thermocline ridge is too deep due to a downwelling Ekman pumping bias related to too weak westerly winds in the equatorial IO (Li et al., 2015a). The equatorial wind biases can be further traced back to biases in simulating the southwest summer monsoon (Li et al., 2015b), illustrating the importance of IO-monsoon interaction.

    The tropical IO has experienced a robust warming since the 1950s——a change due to anthropogenic radiative forcing (Alory et al., 2007; Du and Xie, 2008). While there are some uncertainties in the magnitude and spatial pattern of the IO warming trend in observations (Tokinaga et al., 2012; Han et al., 2014), CMIP5 models project a robust IOD-like warming pattern over the equatorial IO, with anomalous easterlies blowing from the reduced warming in the east to the enhanced warming in the west (Zheng et al., 2013; Christensen et al., 2013). The easterly wind change under global warming deepens the thermocline ridge in the Southwest IO, and can potentially reduce the IPOC persistence. Recent studies have questioned the reliability of the IOD-like projection on the grounds that the easterly errors in the mean wind over the equatorial IO bias Bjerknes feedback too strongly in models (Cai and Cowan, 2013; Li et al., 2016). Consistent with this argument, the variance of the interannual IOD mode is too high in models (Liu et al., 2014).

    The IO is projected to warm more in response to anthropogenic radiative forcing. An early study based on a single model (Zheng et al., 2011) showed that in a warmer climate both the IO warming and AAC persist longer in post-El Niño summer, indicating a strengthening of the positive feedback from the interaction of these interannual ocean-atmosphere anomalies. A similar strengthening of the IPOC mode takes place in a subset of CMIP5 models that are deemed to simulate the mode well in current climate (Chu et al., 2014). (Hu et al., 2014) showed that by changing the moist adiabatic lapse rate, climate warming amplifies the tropospheric Kelvin wave that connects the Indo-western Pacific oceans in post-El Niño summer. Other competing mechanisms, e.g., the increased dry stability of the troposphere acting to reduce the circulation response to latent heating, may cause models to differ in their IPOC response to global warming. Developing a predictive understanding of regional climate change (including modes of variability) is a grand challenge facing the climate research community (Xie et al., 2015), where climate dynamics can be applied and extended.




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