Carton J. A., G. Chepurin, X. H. Cao, and B. Giese, 2000a: A simple ocean data assimilation analysis of the global upper ocean 1950-95. Part I: Methodology. J. Phys. Oceanogr., 30, 294- 309.10.1175/1520-0485(2000)030<0294:ASODAA>2.0.CO;2837e3a61-85f0-4c0c-85a4-849e6d181ca0028821b22106195bee5c3e9b5b76e2b7http://www.researchgate.net/publication/254436070_A_Simple_Ocean_Data_Assimilation_Analysis_of_the_Global_Upper_Ocean_1950_95._Part_I_Methodologyhttp://www.researchgate.net/publication/254436070_A_Simple_Ocean_Data_Assimilation_Analysis_of_the_Global_Upper_Ocean_1950_95._Part_I_MethodologyAbstract The authors describe a 46-year global retrospective analysis of upper-ocean temperature, salinity, and currents. The analysis is an application of the Simple Ocean Data Assimilation (SODA) package. SODA uses an ocean model based on Geophysical Fluid Dynamics Laboratory MOM2 physics. Assimilated data includes temperature and salinity profiles from the World Ocean Atlas-94 (MBT, XBT, CTD, and station data), as well as additional hydrography, sea surface temperature, and altimeter sea level. After reviewing the basic methodology the authors present experiments to examine the impact of trends in the wind field and model forecast bias (referred to in the engineering literature as olored noise). The authors believe these to be the major sources of error in the retrospective analysis. With detrended winds the analysis shows a pattern of warming in the subtropics and cooling in the Tropics and at high latitudes. Model forecast bias results partly from errors in surface forcing and partly from limitations of the model. Bias is of great concern in regions of thermocline water-mass formation. In the examples discussed here, the data assimilation has the effect of increasing production of these water masses and thus reducing bias. Additional experiments examine the relative importance of winds versus subsurface updating. These experiments show that in the Tropics both winds and subsurface updating contribute to analysis temperature, while in midlatitudes the variability results mainly from the effects of subsurface updating.
Carton J. A., G. Chepurin, and X. H. Cao, 2000b: A simple ocean data assimilation analysis of the global upper ocean 1950-95. Part II: Results. J. Phys. Oceanogr., 30, 311- 326.10.1175/1520-0485(2000)0302.0.CO;2007b407a-9aae-4e26-9b7a-50dc45baaf030456de172640ef355266d5b423fbc661http://www.researchgate.net/publication/242099370_A_Simple_Ocean_Data_Assimilation_Analysis_of_the_Global_Upper_Ocean_1950_95._Part_II_Resultshttp://www.researchgate.net/publication/242099370_A_Simple_Ocean_Data_Assimilation_Analysis_of_the_Global_Upper_Ocean_1950_95._Part_II_ResultsAbstract The authors explore the accuracy of a comprehensive 46-year retrospective analysis of upper-ocean temperature, salinity, and currents. The Simple Ocean Data Assimilation (SODA) analysis is global, spanning the latitude range 62°S–62°N. The SODA analysis has been constructed using optimal interpolation data assimilation combining numerical model forecasts with temperature and salinity profiles (MBT, XBT, CTD, and station), sea surface temperature, and altimeter sea level. To determine the accuracy of the analysis, the authors present a series of comparisons to independent observations at interannual and longer timescales and examine the structure of well-known climate features such as the annual cycle, El Ni09o, and the Pacific–North American (PNA) anomaly pattern. A comparison to tide-gauge time series records shows that 25%–35% of the variance is explained by the analysis. Part of the variance that is not explained is due to unresolved mesoscale phenomena. Another part is due to errors in the rate of water mass formation and errors in salinity estimates. Comparisons are presented to altimeter sea level, WOCE global hydrographic sections, and to moored and surface drifter velocity. The results of these comparisons are quite encouraging. The differences are largest in the eddy production regions of the western boundary currents and the Antarctic Circumpolar Current. The differences are generally smaller in the Tropics, although the major equatorial currents are too broad and weak. The strongest basin-scale signal at interannual periods is associated with El Ni09o. Examination of the zero-lag correlation of global heat content shows the eastern and western tropical Pacific to be out of phase (correlation 610.4 to 610.6). The eastern Indian Ocean is in phase with the western Pacific and thus is out of phase with the eastern Pacific. The North Pacific has a weak positive correlation with the eastern equatorial Pacific. Correlations between eastern Pacific heat content and Atlantic heat content at interannual periods are modest. At longer decadal periods the PNA wind pattern leads to broad patterns of correlation in heat content variability. Increases in heat content in the central North Pacific are associated with decreases in heat content in the subtropical Pacific and increases in the western tropical Pacific. Atlantic heat content is positively correlated with the central North Pacific.
Chen B., P. W. Guo, and Y. C. Xiang, 2005: Relationship between summer cross-equatorial flows and ENSO. Journal of Nanjing Institute of Meteorology, 30, 779- 785. (in Chinese)10.1007/s10409-004-0010-x57f2e6cf-253c-4c0c-8ede-42feca6b1328b3334f4b21e8b797c3e36dae1b86f694http%3A%2F%2Fen.cnki.com.cn%2FArticle_en%2FCJFDTOTAL-NJQX200501004.htmrefpaperuri:(80910c2b201425600d1a4445227064f9)http://en.cnki.com.cn/Article_en/CJFDTOTAL-NJQX200501004.htmThe interannual relationships and its interdecadal variabilities between the intensity of summer 850hPa cross-equatorial flows in the Eastern Hemisphere and ENSO are analyzed by using NCEP/NCAR reanalysis data and the sea surface temperatures data of Hadley Center.Results show that Mascarene High was weaker(stronger) and Australia High stronger(weaker) than normal in the El Nino(La Nina) years,which caused summer 850hPa Somali jet was weaker(stronger) and the cross-equatorial flows of about 90°E,105°E,125°E and 150°E were stronger(weaker) than normal.The interannual relationship between Somali jet and ENSO was weakened in the late 1970s while the interannual relationships between the cross-equatorial flows of about 105°E,125°E and 150°E and ENSO were enhanced in the late 1960s.
Cong J., Z. Y. Guan, and L. J. Wang, 2007: Interannual (interdecadal) variabilities of two cross-equatorial flows in association with the Asia summer monsoon variations. Journal of Nanjing Institute of Meteorology, 30( 6), 779- 785. (in Chinese)b809c374-4a2b-4403-b953-9355636ce012bd75b46144edbdc6840fef7512746e32http://en.cnki.com.cn/Article_en/CJFDTotal-NJQX200706007.htmhttp://en.cnki.com.cn/Article_en/CJFDTotal-NJQX200706007.htmThe NCEP/NCAR reanalysis data have been used to study differences between the Somali jet and the cross-equatorial flow at 105E in association with the Asian summer monsoon variations.The results demonstrate that there are significant differences in periodicities as well as the time of climatic jumps of the interannual and interdecadal variations between the two cross-equatorial flows.The strong negative correlations are found between the two cross-equatorial flows in some decades.The Somali jet is closely related to the subsystems including the Indian summer monsoon,East Asian subtropical summer monsoon and South China Sea summer monsoon in the Asian summer monsoon regimes.However,the cross-equatorial flow at 105E is only closely related to the South China Sea summer monsoon variations.The two cross-equatorial flows are found to have different influences on the circulation changes related to different members of the Asian summer monsoon system.
Chakraborty A., R. S. Nanjundiah, and J. Srinivasan, 2009: Impact of African orography and the Indian summer monsoon on the low-level Somali jet. Inter. J. Climatol., 29, 983- 992.10.1002/joc.1720ee73bee5-1873-4159-b03c-149de9e510233d2d0ee3d9ef1374e9679d4a991aac36http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1002%2Fjoc.1720%2Fpdfrefpaperuri:(794e65155a058f25a45e4082490a3156)http://onlinelibrary.wiley.com/doi/10.1002/joc.1720/pdfThe low-level jet (LLJ) over the Indian region, which is most prominent during the monsoon (June-September) season, has been studied with a general circulation model (GCM). The role of African orography in modulating this jet is the focus of this article. The presence of African orography intensifies the cross-equatorial flow. Contrary to previous modelling studies we find that cross-equatorial...
Dai W., Z. N. Xiao, 2014: Multi-time scale variation characteristics of Somali jet and its contact with precipitation in China. Journal of Tropical Meteorology, 30( 2), 368- 376. (in Chinese)eba48c8d-b5ee-4b8a-8957-8fb4fc2d843a8c019bd63d16aaadcd9550636efb8b1ahttp%3A%2F%2Fen.cnki.com.cn%2FArticle_en%2FCJFDTOTAL-RDQX201402018.htmrefpaperuri:(62d0a8727d28963f20a16eb7de5ee873)http://en.cnki.com.cn/Article_en/CJFDTOTAL-RDQX201402018.htmBased on the ERA reanalysis wind data,the multi-time scale activity of Somali Jet is analyzed synthetically and its influences on rainfall in China,including the jet's variations on interannual and interdecadal scales as well as the sub-monthly scale,are also studied using correlation analysis and the composite method.The results demonstrate that there are significant interdecadal variations.The Somali jet became weaker in the 1960s and was the weakest in the early 1970s before increasing slowly in the late 1970s.Moreover,correlations are close between the Somali jet and summer precipitation in China but vary on different time scales.Preliminary analysis shows that the strength variations in May and June during the early days of establishment are well correlated with summer precipitation.The Somali jet intensity on the interdecadal scale is closely related with interdecadal variations of the precipitation in China.Regardless of preceding or simultaneous correlation,the relationship between the Somali jet strength and the rainfall in China's canonical correlation areas show obvious interdecadal variations.Moreover,the link between the intensity anomaly of the jet in the summer-half of the year on the synoptic scale and precipitation processes in China is further discussed.China has more rainfall with positive anomalies but less rainfall with negative anomalies in the main jet activities period in the summer-half of the year,and the positive events influence more on the precipitation in China.
Findlater J., 1969: A major low-level air current near the Indian Ocean during the northern summer. Quart. J. Roy. Meteor. Soc., 95, 362- 380.10.1002/qj.49709540409e4f29171-f0fe-4106-9809-a4663a0f5b6debe8b73e5d364e7499033ca9bad6b40fhttp://onlinelibrary.wiley.com/doi/10.1002/qj.49709540409/citedbyhttp://onlinelibrary.wiley.com/doi/10.1002/qj.49709540409/citedbyABSTRACT It is demonstrated that high-energy flow, in the form of low-level southerly jet streams which have been reported earlier over Kenya, is only one part of a much more extensive current of air which flows rapidly around the western half of the Indian Ocean during the northern summer. The high speeds are associated with the concentration of the cross-equatorial airflow into the zone from longitude 38 deg E to about 55 deg E instead of being rather evenly distributed from 40 deg to 60 deg or 80 deg E as illustrated in many climatological atlases and charts of mean flow during the season. The high-speed current is shown to flow intermittently from the vicinity of Mauritius through Madagascar, Kenya, eastern Ethiopia, Somalia and thence across the Indian Ocean to the west coast of India and beyond. The stream is occasionally reinforced by northward flow through the Mozambique Channel.The high-speed air current, or system of low-level jet streams, is closely associated with the Intertropical Convergence Zone over the Arabian Sea and western India, and variations in the strength of the stream over Kenya during a two month period were related to the rainfall which western India received from the south-west monsoon.
Gruber A., A. F. Krueger, 1984: The status of the NOAA outgoing longwave radiation dataset. Bull. Amer. Meteor. Soc.,65, 958-962, doi: 10.1175/1520-0477(1984)065<0958: TSOTNO>2.0CO;2.10.1175/1520-0477(1984)065<0958:TSOTNO>2.0.CO;28226b67d-d0d8-4228-bd4e-06f48ac9eca53b8dc963be20342031d86e4e81d6377fhttp://ci.nii.ac.jp/naid/10013126152/http://ci.nii.ac.jp/naid/10013126152/Abstract National Oceanic and Atmospheric Administration (NOAA) satellites have provided over eight years of observations from which estimates of the earth's total longwave emittance can be derived. Changes in satellite instrumentation, orbit, and algorithms used in obtaining these estimates are briefly summarized. The algorithms used by NOAA in obtaining a longwave radiation data set are provided.
Gong D. Y., S. W. Wang, 1999: Definition of Antarctic oscillation index. Geophys. Res. Lett., 26, 459- 462.10.1029/1999GL900003d329cda5-493a-4f42-b054-aa78242cc52b1a930f7a6d4125649ea908ceba2f636ehttp%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F1999GL900003%2Fpdfrefpaperuri:(743d7293d5c17596b622cbaf8a4c316e)http://onlinelibrary.wiley.com/doi/10.1029/1999GL900003/pdfFollowing Walker's work about his famous three oscillations published during the 1920–30s, many papers were written about atmospheric oscillations. A fourth atmospheric oscillation in the middle and high southern latitudes was found, and named the Antarctic Oscillation (AO). AO refers to a large scale alternation of atmospheric mass between the mid-latitudes and high latitudes surface pressure. In order to understand the spatial structure of sea level pressure variation in detail, empirical orthogonal function analysis is applied. An objective index of the Antarctic Oscillation Index (AOI) is defined as the difference of zonal mean sea level pressure between 40°S and 65°S. The AOI has the potential for clarifying climate regimes in the southern hemisphere, similar to how the NAO and the NPO has been used in the northern hemisphere.
Gao H., F. Xue, and H. Wang, 2003: Influence of interannual variability of Antarctic oscillation on meiyu along the Yangtze and Huaihe River valley and its importance to prediction. Chinese Science Bulletin, 48, 61- 67. (in Chinese)10.1360/03wd04527003a723-ed3c-4807-a6a1-346c234f4863f4eb71354ece94a85c8d6866bc6d9a18http://www.cnki.com.cn/Article/CJFDTotal-JXTW2003S2009.htmhttp://d.wanfangdata.com.cn/Periodical_kxtb-e2003z2010.aspx Both correlation analysis and case study indi-cate that Antarctic oscillation (AAO) is closely related withsummer rainfall in eastern China. When AAO is stronger inboreal spring, especially in May, there is more mei-yu rain-fall in summer with a longer period along the Yangtze andHuaihe River valley. In contrast, there is less rainfall with ashorter period corresponding to a weaker AAO. Besides, ananomalous AAO changes the position and intensity of severalcirculation systems, which are important to summer rainfallalong the Yangtze and Huaihe River valley. Furthermore, theAntarctic sea ice is negatively correlated with the intensity ofAAO with a 6-month leading time. The result in this studyprovides a new method for the prediction of mei-yu.
Gao H., Y. Y. Liu, Y. G. Wang, and W. J. Li, 2013: Precursory influence of the Antarctic Oscillation on the onset of Asian summer monsoon. Chinese Science Bulletin ,58, 678-683, doi:10.1007/s11434-012-5455-x. (in Chinese)10.1007/s11434-012-5455-x3c725ed0-b895-4926-8aaf-baded80b5202faf99fbef62c9da1f125404a629f5850http%3A%2F%2Fwww.cnki.com.cn%2FArticle%2FCJFDTotal-JXTW201306016.htmrefpaperuri:(5556b8ff4b3bae1fd0d783bc9c5d72fc)http://www.cnki.com.cn/Article/CJFDTotal-JXTW201306016.htm
Halpern D., P. M. Woiceshyn, 2001: Somali jet in the Arabian Sea, El Nio, and India rainfall. J.Climate, 14, 434- 441.10.1175/1520-0442(2001)014<0434:SJITAS>2.0.CO;2ca52aa9f-4ab5-4141-80f6-6ef1a4899ba1ff599e393e77ae1b75b5b70925d92687http://connection.ebscohost.com/c/articles/5436447/somali-jet-arabian-sea-el-nino-india-rainfallhttp://connection.ebscohost.com/c/articles/5436447/somali-jet-arabian-sea-el-nino-india-rainfallABSTRACT Interannual variations of the Somali Jet in the Arabian Sea during 1988-99 were linked to El Nino and La Nina episodes and to India west coast rainfall. Onset dates and monthly mean strengths of the Somali Jet were described with Special Sensor Microwave Imager surface wind speeds. Each year the Somali Jet formed in a similar area in the western Arabian Sea, and always before the onset of monsoon rainfall in Goa. The average date of Somali Jet onset was two days later in El Nino events in comparison with La Nina conditions. Monthly mean strength of the Somali Jet was 0.4 m s[sup -1] weaker during El Nino episodes than during La Nina intervals. When the monthly mean intensity of the Somali Jet was above (below) normal, there was an excess (deficit) of rainfall along the Indian west coast.
Hoerling M. P., J. W. Hurrell, T. Xu, G. T. Bates, and A. S. Phillips, 2004: Twentieth century North Atlantic climate change. Part II: Understanding the effect of Indian Ocean warming. Climate Dyn.,23, 391-405, doi: 10.1007/s00382-004-0433x.10.1007/s00382-004-0433-x18e34a26-c0db-4f63-98d0-e04f2fe46f729456dcff7292f39aed37b60989ce02dahttp://link.springer.com/article/10.1007/s00382-004-0433-xhttp://link.springer.com/article/10.1007/s00382-004-0433-xEnsembles of atmospheric general circulation model (AGCM) experiments are used in an effort to understand the boreal winter Northern Hemisphere (NH) extratropical climate response to the observed warming of tropical sea surface temperatures (SSTs) over the last half of the twentieth Century. Specifically, we inquire about the origins of unusual, if not unprecedented, changes in the wintertime North Atlantic and European climate that are well described by a linear trend in most indices of the North Atlantic Oscillation (NAO). The simulated NH atmospheric response to the linear trend component of tropic-wide SST change since 1950 projects strongly onto the positive polarity of the NAO and is a hemispheric pattern distinguished by decreased (increased) Arctic (middle latitude) sea level pressure. Progressive warming of the Indian Ocean is the principal contributor to this wintertime extratropical response, as shown through additional AGCM ensembles forced with only the SST trend in that sector. The Indian Ocean influence is further established through the reproducibility of results across three different models forced with identical, idealized patterns of the observed warming. Examination of the transient atmospheric adjustment to a sudden witch-on of an Indian Ocean SST anomaly reveals that the North Atlantic response is not consistent with linear theory and most likely involves synoptic eddy feedbacks associated with changes in the North Atlantic storm track. The tropical SST control exerted over twentieth century regional climate underlies the importance of determining the future course of tropical SST for regional climate change and its uncertainty. Better understanding of the extratropical responses to different, plausible trajectories of the tropical oceans is key to such efforts.
Ho C. H., J. H. Kin, C. H. Sui, and D. Y. Gong, 2005: Possible influence of the Antarctic Oscillation on tropical cyclone activity in the western North Pacific. J. Geophys. Res., 110,D19104, doi: 10.1029/2005JD005766.10.1029/2005JD0057668acfeb39-fa0e-4522-aea9-1ed5bd5a47bcd75d8c224862c8e8673b0d51b529659chttp%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2005JD005766%2Fsuppinforefpaperuri:(c0b5948b14cf2f739859b8b866fac362)http://onlinelibrary.wiley.com/doi/10.1029/2005JD005766/suppinfoABSTRACT The present study investigates how large-scale atmospheric circulation in the Southern Hemisphere (SH) modulates tropical cyclone (TC) activity in the western North Pacific (WNP) during a typhoon season (July, August, and September; boreal summer). The variation of the SH circulation of interest is the Antarctic Oscillation (AAO). In the positive phase of AAO relative to its negative phase, two anomalous highs develop over the western Pacific in both hemispheres: a huge anticyclone in southeastern Australia and a relatively weak anticyclone in the East China Sea. These teleconnection patterns are examined and compared with previous analyses. Related to the AAO variations, a statistically significant alteration of TC activities is found over the WNP. The difference in the mean TC passage numbers over the East China Sea (120-140E, 20-40N) between the eight highest-AAO years and the eight lowest-AAO years is as large as 2, equivalent to a 50-100% increase from the climatology. This change is primarily a result of more TCs forming over the eastern Philippine Sea. On the other hand, TC passage numbers slightly decrease over the South China Sea. These changes in TC activity are predominant in August and are consistent with changes in low-level vorticity over the subtropical WNP. The influence of SH circulation variability on large-scale environments and tropical convection in the subtropical NH suggest a possible usage of AAO variation for long-range forecasting of TC activity over the WNP.
Krishnamurti T. N., H. N. Bhalme, 1976: Oscillations of a monsoon system. Part I: Observational aspects. J. Atmos. Sci., 33( 10), 1937- 1954.10.1175/1520-0469(1976)033<1937:OOAMSP>2.0.CO;237a3da21-96c9-4a73-b5cf-204121779c3ee05e7ae3bb2c9e3b6268532bb29826cbhttp://www.researchgate.net/publication/234339249_Oscillations_of_a_Monsoon_System._Part_I._Observational_Aspectshttp://www.researchgate.net/publication/234339249_Oscillations_of_a_Monsoon_System._Part_I._Observational_AspectsAbstract In this paper the elements of a monsoon system are defined, and its oscillations are determined from spectral analysis of long observational records. The elements of the monsoon system include pressure of the monsoon trough, pressure of the Mascarene high, cross-equatorial low-level jet, Tibetan high, tropical easterly jet, monsoon cloud cover, monsoon rainfall, dry static stability of the lower troposphere, and moist static stability of the lower troposphere. The summer monsoon months over India during normal monsoon rainfall years are considered as guidelines in the selection of data for the period of this study. The salient result of this study is that there seems to exist a quasi-biweekly oscillation in almost all of the elements of the monsoon system. For some of these elements, such as the surface pressure field, monsoon rainfall, low-level cross-equatorial jet and monsoon cloudiness, the amplitude of this oscillation in quasi-biweekly range is very pronounced. For the spectral representation of the time series, the product of the spectral density times frequency is used as the ordinate and the log of the frequency as the abscissa. Dominant modes are also found in the shorter time scales (<6 days). A sequential ordering of elements of the monsoon systems for the quasi-biweekly oscillation is carried out in terms of their respective phase angle. The principal result here is that soon after the maximum dry and moist static instabilities are realized in the stabilizing phase, there occur in sequence an intensification of the monsoon trough, satellite brightness, Mascarene high, Tibetan high and the tropical easterly jet. Soon after that the rainfall maximum over central India, arising primarily from monsoon depressions, is found to be a maximum. In the second part of this paper we offer some plausible mechanisms for these quasi-biweekly oscillations.
Krishnamurti T. N., J. Molinari, and H. L. Pan, 1976: Numerical simulation of the Somali jet. J. Atmos. Sci., 33, 2350- 2362.10.1175/1520-0469(1976)0332.0.CO;24fbe41ea-0f33-49eb-92fd-10fac65756a01cd2c41c645ef8f6dee83f722a69aa1chttp%3A%2F%2Fci.nii.ac.jp%2Fncid%2FBA46969972refpaperuri:(d4c293052d60660f8dc63aa344760a10)http://ci.nii.ac.jp/ncid/BA46969972Abstract In this study we show that many of the observed features of the cross-equatorial low-level jet of the Arabian Sea, Indian Ocean and Somalia can be numerically simulated by including 1) the cast African and Madagascar mountains, 2) the beta effect and 3) a lateral forcing from the east around 75°E. This lateral forcing at 75°E is, in fact, a solution of another numerical model–one where the land-ocean contrast heating in the meridional direction is incorporated in much detail to simulate the zonally symmetric monsoons, essentially following Murakami et al . (1970). This zonally symmetric solution of a very long-term numerical integration from a state of rest exhibits many of the observed characteristics of the broad-scale monsoons at 75°E. This later solution is used as a lateral forcing for the low-level jet simulations over the Arabian Sea-Indian Ocean. The numerical model presented here is a one-level primitive equation model with a detailed bottom topography and a one-degree latitude grid size. Results of several controlled numerical experiments suppressing or including orography, the beta effect and the broad-scale lateral monsoon forcing at 75°E are discussed in this paper. When all the three above-mentioned parameters are included, features such as strong winds just downstream from the Madagascar mountains, an equatorial relative speed minimum, an intense jet off the Somali coast and a split of the jet over the northern Arabian Sea are simulated from an initial state of rest. The Ethiopian highland appears crucial for the simulation of the Somali coast strong winds; the Madagascar mountains are most important for the strong winds just downstream from Madagascar. The split in the jet over the Arabian Sea is analyzed as a barotropic instability problem. The beta effect is essential for the simulation of the observed geometry. Experiments with a weak broad-scale monsoon forcing at 75°E fall to produce strong winds over cast Africa. The implications of this forcing are analyzed in this paper and some relevant observations are presented.
Kalnay, E., Coauthors, 1996: The NCEP/NCAR 40-year reanalysis project. Bull. Amer. Meteor. Soc.,77, 437-471, doi: 10.1175/1520-0477(1996)077<0437:TNYRP>2.0.CO;2.10.1175/1520-0477(1996)0772.0.CO;24f641748c1fe7c7d954de7018f8e59a5http%3A%2F%2Fci.nii.ac.jp%2Fnaid%2F10013127325%2Fhttp://ci.nii.ac.jp/naid/10013127325/Abstract The NCEP and NCAR are cooperating in a project (denoted “reanalysis”) to produce a 40-year record of global analyses of atmospheric fields in support of the needs of the research and climate monitoring communities. This effort involves the recovery of land surface, ship, rawinsonde, pibal, aircraft, satellite, and other data; quality controlling and assimilating these data with a data assimilation system that is kept unchanged over the reanalysis period 1957–96. This eliminates perceived climate jumps associated with changes in the data assimilation system. The NCEP/NCAR 40-yr reanalysis uses a frozen state-of-the-art global data assimilation system and a database as complete as possible. The data assimilation and the model used are identical to the global system implemented operationally at the NCEP on 11 January 1995, except that the horizontal resolution is T62 (about 210 km). The database has been enhanced with many sources of observations not available in real time for operations, provided by different countries and organizations. The system has been designed with advanced quality control and monitoring components, and can produce 1 mon of reanalysis per day on a Cray YMP/8 supercomputer. Different types of output archives are being created to satisfy different user needs, including a “quick look” CD-ROM (one per year) with six tropospheric and stratospheric fields available twice daily, as well as surface, top-of-the-atmosphere, and isentropic fields. Reanalysis information and selected output is also available on-line via the Internet (http//:nic.fb4.noaa.gov:8000). A special CD-ROM, containing 13 years of selected observed, daily, monthly, and climatological data from the NCEP/NCAR Re-analysis, is included with this issue. Output variables are classified into four classes, depending on the degree to which they are influenced by the observations and/or the model. For example, “C” variables (such as precipitation and surface fluxes) are completely determined by the model during the data assimilation and should be used with caution. Nevertheless, a comparison of these variables with observations and with several climatologies shows that they generally contain considerable useful information. Eight-day forecasts, produced every 5 days, should be useful for predictability studies and for monitoring the quality of the observing systems. The 40 years of reanalysis (1957–96) should be completed in early 1997. A continuation into the future through an identical Climate Data Assimilation System will allow researchers to reliably compare recent anomalies with those in earlier decades. Since changes in the observing systems will inevitably produce perceived changes in the climate, parallel reanalyses (at least 1 year long) will be generated for the periods immediately after the introduction of new observing systems, such as new types of satellite data. NCEP plans currently call for an updated reanalysis using a state-of-the-art system every five years or so. The successive reanalyses will be greatly facilitated by the generation of the comprehensive database in the present reanalysis.
Lei X. C., X. Q. Yang, 2008: Interannual variation characteristic of east hemispheric cross-equatorial flow and its contemporaneous relationships with temperature and rainfall in China. Journal of Tropical Meteorology, 24( 2), 127- 135. (in Chinese)
Li C., S. L. Li, 2014: Interannual seesaw between the Somali and the Australian cross-equatorial flows and its connection to the East Asian Summer Monsoon. J. Climate,27, 3966-3981, doi: 10.1175/JCLI-D-13-00288.1.
Nan S. L., J. P. Li, 2003: The relationship between the summer precipitation in the Yangtze River valley and the boreal spring Southern Hemisphere Annular Mode. Geophys. Res. Lett., 30(24),2266, doi: 10.1029/2003GL018381.10.1029/2003GL018381b9df73e4-e151-42b0-a83b-96a13198756cf3b5982070e6bad90b1e3681355a6a35http://onlinelibrary.wiley.com/doi/10.1029/2003GL018381/abstract;jsessionid=293B917A5F204DF0610690D0668A406C.f04t01http://onlinelibrary.wiley.com/doi/10.1029/2003GL018381/abstract;jsessionid=293B917A5F204DF0610690D0668A406C.f04t01The relationship between the boreal spring (April-May) Southern Hemisphere annular mode (SAM) and the following summer (June-August) precipitation in China for the period of 1951-2001 is examined statistically in this study. There is a significantly positive correlation between the boreal spring SAM index (SAMI) and the following summer rainfall in the middle and lower reaches of the Yangtze River. The summer large-scale atmospheric circulation anomalies over East Asia are also related to the boreal spring SAMI events. A strong SAM in boreal spring is followed by a weakened East Asian summer monsoon, a strengthened and westward expanded western Pacific subtropical high (WPSH), as well as increased ascending vertical velocity, specific humidity and water vapor flux convergence. These situations provide necessary circulation and water vapor conditions for increasing the summer precipitation in the middle and lower reaches of the Yangtze River valley, and vice versa. The boreal spring SAM variation provides a potential valuable signal for predicting the summertime precipitation in the middle and lower reaches of the Yangtze River valley.
Nan S. L., J. P. Li, X. J. Yuan, and P. Zhao, 2009: Boreal spring Southern Hemisphere Annular Mode, Indian Ocean sea surface temperature, and East Asian summer monsoon. J. Geophys. Res., 114,D02103, doi: 10.1029/2008JD010045.10.1029/2008JD010045be8177fd-58a8-4492-9830-15de74a8d3069d02e25859916fa3c91db58cd5e749a4http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2008JD010045%2Fabstractrefpaperuri:(1f35b192d839daa62e8c3082d8abea1e)http://onlinelibrary.wiley.com/doi/10.1029/2008JD010045/abstract[1] The relationships among the boreal spring Southern Hemisphere Annular Mode (SAM), the Indian Ocean (IO) sea surface temperature (SST), and East Asian summer monsoon (EASM) are examined statistically in this paper. The variability of boreal spring SAM is closely related to the IO SST. When the SAM is in its strong positive phase in boreal spring, with low-pressure anomalies over the south pole and high-pressure anomalies over middle latitudes, SST over the subtropics and middle latitudes of the South Indian Ocean (SIO) increases, which persists into the summer. Following the positive SST anomalies over the subtropics and midlatitudes of the SIO, SST in the equatorial Indian Ocean and Bay of Bengal increases in summer. Moreover, the variability of SST in the equatorial Indian Ocean and Bay of Bengal is closely related to EASM. When SST in the equatorial Indian Ocean and Bay of Bengal increases, EASM tends to be weak. Therefore the IO SST may play an important role bridging boreal spring SAM and EASM. The atmospheric circulations and surface heat exchanges contribute to the SST anomalies in the SIO. When the spring SAM is in its strong positive phases, the regional Ferrel Cell weakens, and the anomalous upward motions at 20°S–30°S cause an increase of low cloud cover and downward longwave radiation flux. The surface atmospheric circulations also transport more (less) warmer (cooler) air from middle latitudes north of 50°S (high latitudes south of 60°S) into 50°S–60°S and warm the air, which reduces the temperature difference between the ocean and atmosphere and consequently reduces sensible heat flux from the ocean to atmosphere. The increased downward longwave radiation and decreased sensible heat are responsible for the SST increase in the SIO. The atmospheric circulation and surface heat flux anomalies are of opposite signs following the strong negative phases of SAM.
Neale, R. B., Coauthors, 2010: Description of the NCAR Community Atmosphere Model (CAM5.0), NCAR Technical Note. [Available online at http://www.cesm.ucar.edu/models/cesm1.0/cam/docs/description/cam5desc.pdf.]96fa8938727198f968945b80877df9adhttp://www.researchgate.net/publication/224017878_Description_of_the_NCAR_Community_Atmosphere_Modelhttp://www.researchgate.net/publication/224017878_Description_of_the_NCAR_Community_Atmosphere_ModelThe Technical Note series provides an outlet for a variety of NCAR manuscripts that contribute in specialized ways to the body of scientific knowledge but which are not suitable for journal, monograph, or book publication. Reports in this series are issued by the NCAR Scientific Divisions; copies may be obtained on request from the Publications Office of NCAR. Designation symbols for the series include: EDD: IA: PPR: Engineering, Design, or Development Reports Equipment descriptions, test results, instrumentation, and operating and maintenance manuals. Instructional Aids Instruction manuals, bibliographies, film supplements, and other research or instructional aids. Program Progress Reports Field program reports, interim and working reports, survey reports, and plans for experiments. PROC: Proceedings Documentation of symposia, colloquia, conferences, workshops, and lectures. (Distribution may be limited to attendees.) STR: Scientific and Technical Reports Data compilations, theoretical and numerical
Ramanathan V., R. D. Cess, E. F. Harrison, P. Minnis, B. R. Barkstrom, E. Ahmad, and D. Hartmann, 1989: Cloud-radiative forcing and climate: Results from the Earth Radiation Budget Experiment. Science, 243( 4887), 57- 63.10.1126/science.243.4887.5717780422fe52ec37-db42-4e4c-9e4e-3067649aa8ef9aa1f2ecf2821401a087d632af5d67e0http%3A%2F%2Fmed.wanfangdata.com.cn%2FPaper%2FDetail%2FPeriodicalPaper_PM17780422refpaperuri:(9f211c0a401f4035e91112d50b5cf55b)http://med.wanfangdata.com.cn/Paper/Detail/PeriodicalPaper_PM17780422The study of climate and climate change is hindered by a lack of information on the effect of clouds on the radiation balance of the earth, referred to as the cloud-radiative forcing. Quantitative estimates of the global distributions of cloud-radiative forcing have been obtained from the spaceborne Earth Radiation Budget Experiment (ERBE) launched in 1984. For the April 1985 period, the global shortwave cloud forcing [-44.5 watts per square meter (W/m(2))] due to the enhancement of planetary albedo, exceeded in magnitude the longwave cloud forcing (31.3 W/m(2)) resulting from the greenhouse effect of clouds. Thus, clouds had a net cooling effect on the earth. This cooling effect is large over the mid-and high-latitude oceans, with values reaching -100 W/m(2). The monthly averaged longwave cloud forcing reached maximum values of 50 to 100 W/m(2) over the convectively disturbed regions of the tropics. However, this heating effect is nearly canceled by a correspondingly large negative shortwave cloud forcing, which indicates the delicately balanced state of the tropics. The size of the observed net cloud forcing is about four times as large as the expected value of radiative forcing from a doubling of CO(2). The shortwave and longwave components of cloud forcing are about ten times as large as those for a CO(2) doubling. Hence, small changes in the cloud-radiative forcing fields can play a significant role as a climate feedback mechanism. For example, during past glaciations a migration toward the equator of the field of strong, negative cloud-radiative forcing, in response to a similar migration of cooler waters, could have significantly amplified oceanic cooling and continental glaciation.
Ramanathan V., B. Subasilar, G. J. Zhang, W. Conant, R. D. Cess, J. T. Kiehi, H. Grassi, and L. Shi, 1995: Warm pool heat budget and shortwave cloud forcing: A missing physics? Science, 267( 5197), 499- 503.10.1126/science.267.5197.499177887845f6fbbc0-7667-47cb-ba53-3f53afd6cbe8639c9f9a3fd58d88374090d131fca210http://med.wanfangdata.com.cn/Paper/Detail/PeriodicalPaper_PM17788784http://med.wanfangdata.com.cn/Paper/Detail/PeriodicalPaper_PM17788784Ship observations and ocean models indicate that heat export from the mixed layer of the western Pacific warm pool is small (<20 watts per square meter). This value was used to deduce the effect of clouds on the net solar radiation at the sea surface. The inferred magnitude of this shortwave cloud forcing was large ( approximately - 100 watts per square meter) and exceeded its observed value at the top of the atmosphere by a factor of about 1.5. This result implies that clouds (at least over the warm pool) reduce net solar radiation at the sea surface not only by reflecting a significant amount back to space, but also by trapping a large amount in the cloudy atmosphere, an inference that is at variance with most model results. The excess cloud absorption, if confirmed, has many climatic implications, including a significant reduction in the required tropics to extrattropics heat transport in the oceans.
Rodwell M. J., B. J. Hoskins, 1995: A model of the Asian summer monsoon. Part II: Cross-equatorial flow and PV behavior. J. Atmos. Sci., 52, 1341- 1356.10.1175/1520-0469(1995)0522.0.CO;24ae5107e-54c8-4ed1-952b-303ce0b27081baa92009083a4f2cba49ce7ae348df29http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F252286372_A_Model_of_the_Asian_Summer_Monsoon.Part_II_Cross-Equatorial_Flow_and_PV_Behavior%3Fev%3Dauth_pubrefpaperuri:(22d77354c6f98718565b832a3acc0f5b)http://www.researchgate.net/publication/252286372_A_Model_of_the_Asian_Summer_Monsoon.Part_II_Cross-Equatorial_Flow_and_PV_Behavior?ev=auth_pubPart II. Investigates the mechanisms that sustain the low-level East African Jet by using the model developed and tested in part I of `A model of the Asian summer monsoon'. Potential vorticity equation and material modification of potential vorticity (PV); Importance of the East African Highlands and a land/sea contrast in surface friction; Examination of PV behavior.
Smith T. M., R. W. Reynolds, 2004: Improved extended reconstruction of SST (1854-1997). J.Climate, 17, 2466- 2477.10.1175/1520-0442(2004)017<2466:IEROS>2.0.CO;2be77fef9-7a63-49c9-84dc-a6fa6254268f942af804e3fb7c909af1189191bf1769http://www.researchgate.net/publication/249611561_Improved_Extended_Reconstruction_of_SST_(18541997)http://www.researchgate.net/publication/249611561_Improved_Extended_Reconstruction_of_SST_(18541997)Abstract An improved SST reconstruction for the 1854–1997 period is developed. Compared to the version 1 analysis, in the western tropical Pacific, the tropical Atlantic, and Indian Oceans, more variance is resolved in the new analysis. This improved analysis also uses sea ice concentrations to improve the high-latitude SST analysis and a modified historical bias correction for the 1939–41 period. In addition, the new analysis includes an improved error estimate. Analysis uncertainty is largest in the nineteenth century and during the two world wars due to sparse sampling. The near-global average SST in the new analysis is consistent with the version 1 reconstruction. The 95% confidence uncertainty for the near-global average is 0.4°C or more in the nineteenth century, near 0.2°C for the first half of the twentieth century, and 0.1°C or less after 1950.
Shi W. J., Z. N. Xiao, 2013: Variation of the cross-equatorial moisture transport in Somali and its impact on china early summer rainfall in nearly 60 years. Meteorological Monthly, 39, 39- 45. (in Chinese)629efa8b-1985-415f-a96d-3e30cac6f394a188d280a74619fbd61f02d4831ef23dhttp%3A%2F%2Fen.cnki.com.cn%2FArticle_en%2FCJFDTOTAL-QXXX201301006.htmrefpaperuri:(402aecb363f29b5ff0943e96233f9141)http://en.cnki.com.cn/Article_en/CJFDTOTAL-QXXX201301006.htmBased on the NCEP / NCAR wind field,specific humidity,surface pressure and precipitation reanalysis data from 1951 to 2010,a cross-equatorial moisture transport intensity index is established to characterize the strength of the Somali jet(SMJ),and the seasonal,interannual,decadal variations and mutations of the SMJ cross-equatorial moisture transport intensity are studied,while comparing with the traditional SMJ wind speed intensity index.In addition,the relationship between SMJ and the China early summer precipitation is analyzed.Based on the above analysis,the decadal changes of this relationship are revealed.Main results are as follows.After the 1990s,the SMJ wind speed intensity index is weakening, but the SMJ water vapor transport has no significant variations;compared with the SMJ wind speed strength,the SMJ water vapor transmission intensity is associated with the China early summer rainfall more closely.When the SMJ is weaker,rainfall decreased in the Huanghe-Huaihe River Basin and North China in early summer,and vice versa.Besides,this correlation has been strengthened in recent 30 years.
Shi W. J., Z. N. Xiao, 2014: Impact of the preceding boreal winter Southern Annular Mode on the summertime Somali Jet. Atmos. Oceanic Sci. Lett.,7, 534-539, doi: 10.3878/ AOSL20140045.10.3878/AOSL20140045e8ac555e-4280-4120-920a-782a1f379b1f4fab8347ef5d7b4a6c34e15c7ce9eb46http%3A%2F%2Fwww.cnki.com.cn%2FArticle%2FCJFDTotal-AOSL201406010.htmrefpaperuri:(488580705b3c20666c7177256c49c572)http://d.wanfangdata.com.cn/Periodical_dqhhykxkb201406010.aspx
Tao W. K., S. Lang, J. Simpson, C. H. Sui, B. Ferrier, and M. D. Chou, 1996: Mechanisms of cloud-radiation interaction in the tropics and midlatitudes. J. Atmos. Sci., 53( 18), 2624- 2651.10.1175/1520-0469(1996)0532.0.CO;291f4cf43-8933-4560-9f50-cc10480b858bf033efe01c0a577ef84b2818cf1db141http%3A%2F%2Fconnection.ebscohost.com%2Fc%2Farticles%2F9704046788%2Fmechanisms-cloud-radiation-interaction-tropics-midlatitudesrefpaperuri:(4a95cd040bbe2f2402b893a9ea87f038)http://connection.ebscohost.com/c/articles/9704046788/mechanisms-cloud-radiation-interaction-tropics-midlatitudesAbstract Radiative forcing and latent heat associated with precipitation are the two most important diabatic processes that drive the circulation of the atmosphere. Clouds can affect radiation and vice versa. It is known that longwave radiative processes can enhance precipitation in cloud systems. This paper concentrates on determining the relative importance of three specific longwave radiative mechanisms by comparing cloud-resolving models with and without one or more of these processes. Three of the ways that longwave radiation is thought to interact with clouds are as follows: 1) cloud-top cooling and cloud-base warming may alter the thermal stratification of cloud layers, 2) differential cooling between clear and cloudy regions might enhance convergence into the cloud system, and 3) large-scale cooling could change the environment. A two-dimensional version of the Goddard Cumulus Ensemble model has been used to perform a series of sensitivity tests to identify which is the dominant cloud-radiative forcing mechanism with respect to the organization, structure, and precipitation processes for both a tropical (EMEX) and a midlatitude (PRE-STORM) mesoscale convective system. The model results indicate that the dominant process for enhancing the surface precipitation in both the PRE-STORM and EMEX squall cases is the large-scale radiative cooling. However, the overall effect is really to increase the relative humidity and not tie convective available potential energy (CAPE). Because of the high moisture in the Tropics, the increase in relative humidity by radiative cooling can have more of an impact on precipitation in the tropical case than in the midlatitude case. The large-scale cooling led to a 36% increase in rainfall for the tropical cast. The midlatitude model squall with a higher CAPE and lower humidity environment was only slightly affected (8%) by any of the longwave mechanisms. Our results also indicated that the squall systems' overall (convective and stratiform) precipitation is increased by turning off the cloud-top cooling and cloud-base warming. Therefore, the cloud-top cooling-cloud-base warming mechanism was not the responsible cloud-radiative mechanism for enhancing the surface precipitation. However, the circulation as well as the microphysical processes were indeed (slightly) enhanced in the stratiform region by the cloud-top cooling and cloud-base warming mechanism for the midlatitude squall case. For both cases, the model results show that the mechanism associated with differential cooling between the clear and cloudy regions may or may not enhance precipitation processes. However, this mechanism is definitely less important than the large-scale longwave radiative cooling. Solar heating was run from 0900 to 1300 LST in both environments and was found to decrease the precipitation by 7% in each case compared to the runs with longwave radiation only. This result suggests that solar heating may play a significant role in the daytime minimum/nighttime maximum precipitation cycle found over most oceans.
Thompson D. W. J., J. M. Wallace, 2000: Annular modes in the extratropical circulation. Part I: Month-to-month variability. J.Climate, 13, 1000- 1016.10.1175/1520-0442(2000)0132.0.CO;20e5d40a8-933b-4a70-a32b-5b5ebb805f871383c8724bdfb1521bb16b3014fa8eb5http://ci.nii.ac.jp/naid/10013127396/http://ci.nii.ac.jp/naid/10013127396/The leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep, zonally symmetric or "annular" structures, with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude. The structure and dynamics of the Southern Hemisphere (SH) annular mode have been extensively documented, whereas the existence of a Northern Hemisphere (NH) mode, herein referred to as the Arctic Oscillation (AO), has only recently been recognized. Like the SH mode, the AO can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields. In this paper the structure and seasonality of the NH and SH modes are compared based on data from the National Centers for Environmental Prediction--National Center for Atmospheric Research reanalysis and supplementary datasets. The structures of the NH and SH annular modes are shown to be remarkably similar, not only in the zonally averaged geopotential height and zonal wind fields, but in the mean meridional circulations as well. Both exist year-round in the troposphere, but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave--mean flow interaction: midwinter in the NH and late spring in the SH. During these "active seasons," the annular modes modulate the strength of the Lagrangian mean circulation in the lower stratosphere, total column ozone and tropopause height over mid- and high latitudes, and the strength of the trade winds of their respective hemispheres. The NH mode also contains an embedded planetary wave signature with expressions in surface air temperature, precipitation, total column ozone, and tropopause height. It is argued that the horizontal temperature advection by the perturbed zonal-mean zonal wind...
Uppala, S. M., Coauthors, 2005: The ERA-40 re-analysis. Quart. J. Roy. Meteor. Soc.,131, 2961-3012, doi: 10.1256/qj. 04.176.10.1256/qj.04.176f7b5a09c-bed4-47e2-9010-855ba65488a16cd9415ab29e0a6ea3317250b2bd918ahttp://onlinelibrary.wiley.com/doi/10.1256/qj.04.176/pdfhttp://onlinelibrary.wiley.com/doi/10.1256/qj.04.176/pdfAbstract ERA-40 is a re-analysis of meteorological observations from September 1957 to August 2002 produced by the European Centre for Medium-Range Weather Forecasts (ECMWF) in collaboration with many institutions. The observing system changed considerably over this re-analysis period, with assimilable data provided by a succession of satellite-borne instruments from the 1970s onwards, supplemented by increasing numbers of observations from aircraft, ocean-buoys and other surface platforms, but with a declining number of radiosonde ascents since the late 1980s. The observations used in ERA-40 were accumulated from many sources. The first part of this paper describes the data acquisition and the principal changes in data type and coverage over the period. It also describes the data assimilation system used for ERA-40. This benefited from many of the changes introduced into operational forecasting since the mid-1990s, when the systems used for the 15-year ECMWF re-analysis (ERA-15) and the National Centers for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) re-analysis were implemented. Several of the improvements are discussed. General aspects of the production of the analyses are also summarized. A number of results indicative of the overall performance of the data assimilation system, and implicitly of the observing system, are presented and discussed. The comparison of background (short-range) forecasts and analyses with observations, the consistency of the global mass budget, the magnitude of differences between analysis and background fields and the accuracy of medium-range forecasts run from the ERA-40 analyses are illustrated. Several results demonstrate the marked improvement that was made to the observing system for the southern hemisphere in the 1970s, particularly towards the end of the decade. In contrast, the synoptic quality of the analysis for the northern hemisphere is sufficient to provide forecasts that remain skilful well into the medium range for all years. Two particular problems are also examined: excessive precipitation over tropical oceans and a too strong Brewer-Dobson circulation, both of which are pronounced in later years. Several other aspects of the quality of the re-analyses revealed by monitoring and validation studies are summarized. Expectations that the &lsquo;second-generation&rsquo; ERA-40 re-analysis would provide products that are better than those from the firstgeneration ERA-15 and NCEP/NCAR re-analyses are found to have been met in most cases. Royal Meteorological Society, 2005. The contributions of N. A. Rayner and R. W. Saunders are Crown copyright.
Ummenhofer C. C., A. S. Gupta, M. J. Pook, and M. H. England, 2008: Anomalous rainfall over southwest Western Australia forced by Indian Ocean sea surface temperatures. J.Climate, 21, 5113- 5134.10.1175/2008JCLI2227.172e5baea-fd29-4d2a-8e65-af9e5f3832de74100143efe06940e775dfe3f6124a71http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F253868482_Anomalous_Rainfall_over_Southwest_Western_Australia_Forced_by_Indian_Ocean_Sea_Surface_Temperaturesrefpaperuri:(c3fb92547efb8aa5ae73b1a19bc2853d)http://www.researchgate.net/publication/253868482_Anomalous_Rainfall_over_Southwest_Western_Australia_Forced_by_Indian_Ocean_Sea_Surface_TemperaturesThe potential impact of Indian Ocean sea surface temperature (SST) anomalies in modulating midlatitude precipitation across southern and western regions of Australia is assessed in a series of atmospheric general circulation model (AGCM) simulations. Two sets of AGCM integrations forced with a seasonally evolving characteristic dipole pattern in Indian Ocean SST consistent with observed 17dry year17 (PDRY) and 17wet year17 (PWET) signatures are shown to induce precipitation changes across western regions of Australia. Over Western Australia, a significant shift occurs in the winter and annual rainfall frequency with the distribution becoming skewed toward less (more) rainfall for the PDRY (PWET) SST pattern. For southwest Western Australia (SWWA), this shift primarily is due to the large-scale stable precipitation. Convective precipitation actually increases in the PDRY case over SWWA forced by local positive SST anomalies. A mechanism for the large-scale rainfall shifts is proposed, by which the SST anomalies induce a reorganization of the large-scale atmospheric circulation across the Indian Ocean basin. Thickness (100017500 hPa) anomalies develop in the atmosphere mirroring the sign and position of the underlying SST anomalies. This leads to a weakening (strengthening) of the meridional thickness gradient and the subtropical jet during the austral winter in PDRY (PWET). The subsequent easterly offshore (westerly onshore) anomaly in the thermal wind over southern regions of Australia, along with a decrease (increase) in baroclinicity, results in the lower (higher) levels of large-scale stable precipitation. Variations in the vertical thermal structure of the atmosphere overlying the SST anomalies favor localized increased convective activity in PDRY because of differential temperature lapse rates. In contrast, enhanced widespread ascent of moist air masses associated with frontal movement in PWET accounts for a significant increase in rainfall in that ensemble set.
Wang H. J., F. Xue, 2003: Interannual variability of Somali jet and its influences on the inter-hemispheric water vapor transport and on the East Asian summer rainfall. Chinese Journal of Geophysics, 46, 18- 25. (in Chinese)10.3321/j.issn:0001-5733.2003.01.0032fc96055-17dd-492f-a061-86cccd9101186607d45597ac38c8de28618219608cf0http%3A%2F%2Fwww.oalib.com%2Fpaper%2F1567706refpaperuri:(757d01227a274ad40a2817bd4621f8eb)http://www.oalib.com/paper/1567706The monthly reanalysis data set and the analyzed precipitation data set are used to study the interannual variability of Somali Jet (SMJ) and its influences on the inter-hemispheric water vapor transport and on the East Asian summer climate. It is indicated that SMJ plays a key role in the water vapor transport between the two hemispheres. SMJ transports water vapor through the equator from the southern hemisphere to the northern hemisphere during boreal summer time, and from northern hemisphere to the southern hemisphere during boreal winter time. The interannual variation of SMJ is found to be linked with the many changes around the globe, including the wave pattern along East Asia coast, the South Asian high, and dipole pattern to the southeast of Australia. The results also reveal that interannual variation of SMJ at boreal spring has significant influences on the East Asian summer rainfall and atmospheric circulation. Since the changes of SMJ precede the changes of East Asian summer climate, these findings may help to improve the summer climate prediction in East Asia.
Wu Z. W., J. P. Li, B. Wang, and X. H. Liu, 2009: Can the Southern Hemisphere annular mode affect China winter monsoon? J. Geophys. Res., 114,D11107, doi: 10.1029/2008JD011501.10.1029/2008JD011501d96144ac-a8c2-4c95-be9f-ff08f9f8e9e6547392fb6146fe62af56cdcb9395ee8ahttp%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2008JD011501%2Fcitedbyrefpaperuri:(176e37eb5f9a90da69f38d0091e1852b)http://onlinelibrary.wiley.com/doi/10.1029/2008JD011501/citedby[1] Many previous studies suggested that the anomalous Northern Hemisphere annular mode (NAM) and associated low boundary forcing (e.g., snow cover) greatly influence the China winter monsoon (CWM) variability on interannual to inter-decadal timescales. In this article, it is found that the Southern Hemisphere annular mode (SAM) also well correlates with the two observed CWM major modes, which has not been revealed before. Note that the two CWM major modes are obtained by performing Empirical Orthogonal Function (EOF) analysis on winter surface air temperature at 160 gauge stations across China for the 1951-2006 period. They explain around 70% of the total CWM variances. The first EOF mode exhibits a homogeneous spatial pattern with the corresponding principal component displaying a significant inter-decadal variation, which reflects the warming trend in China during the past 56 years. The second EOF mode shows a meridional seesaw pattern and is basically associated with significant interannual variations. Both of the leading modes are intimately associated with the simultaneous SAM-like hemispheric circulation anomalies. Moreover, the SAM-like anomalies signal precursory conditions for the first CWM mode in boreal autumn. The relevant physical mechanisms by which anomalous autumn SAM may affect the CWM are investigated with NCAR Community Atmospheric Model version 3 (CAM3). When SAM is in a strong phase during boreal autumn, the circum-Antarctic upper level jet stream displaces poleward and the corresponding surface wind speeds reduce in the region between 45S and 30S, inducing a hemispheric-scale warm sea surface temperature (SST) belt beneath. Such an anomalously warm SST belt persists through boreal winter and weakens the Hadley cell. The weakened Hadley cell in boreal winter corresponds to anomalous southerlies prevailing in the lower troposphere over China, which favor a weak CWM. The intimate linkage between the autumn SAM and CWM may be instrumental for understanding interactions between the Northern and Southern Hemisphere and can provide a way to predict the CWM variations.
Wu Z., J. Li, Z. Jiang, and T. Ma, 2012: Modulation of the Tibetan Plateau snow cover on the ENSO teleconnections: From the East Asian summer monsoon perspective. J.Climate, 25, 2481- 2489.10.1175/JCLI-D-11-00135.1d13015a5-efe9-4b1f-b724-0eedf9f79d437e9a7a51359fec990816517fa858932bhttp%3A%2F%2Fwww.researchgate.net%2Fpublication%2F258373651_Modulation_of_the_Tibetan_Plateau_Snow_Cover_on_the_ENSO_Teleconnections_From_the_East_Asian_Summer_Monsoon_Perspective%3Fev%3Dauth_pubrefpaperuri:(c6cc36eac685d89a9e16e3ab5bdd3932)http://www.researchgate.net/publication/258373651_Modulation_of_the_Tibetan_Plateau_Snow_Cover_on_the_ENSO_Teleconnections_From_the_East_Asian_Summer_Monsoon_Perspective?ev=auth_pubAbstract The East Asian summer monsoon (EASM) may exhibit rather large variability between years characterized by the same ENSO phase. Such inconsistency reduces the EASM predictability based on ENSO. Results in this study show that the Tibetan Plateau snow cover (TPSC) exerts a modulating effect on ENSO teleconnections and ENSO significantly correlates with the EASM only during the reduced TPSC summers. Three-dimensional circulation structures are examined to manifest that the typical ENSO signals in reduced TPSC summers tend to be stronger than in excessive TPSC summers. Numerical and theoretical evidences indicate that the anomalously reduced TPSC can force positive geopotential height anomalies at the upper troposphere and weaken the jet streams across eastern Asia and northwestern Pacific. Governed by such basic state zonal flows, the extratropical Rossby wave response to the ENSO forcing usually has a larger amplitude and pronounced westward development. In such case, ENSO extends its influences to eastern Asia and enhances its connection with the EASM.
Wu Z. W., J. Dou, and H. Lin, 2015: Potential influence of the November-December Southern Hemisphere annular mode on the East Asian winter precipitation: A new mechanism. Climate Dyn.,44, 1215-1226, doi: 10.1007/s00382-014-2241-2.10.1007/s00382-014-2241-28db955a4-453c-4f63-8c3b-573676d4c4953f52fe3421e93cd3ea77248cd1022db1http://www.springerlink.com/content/fulltext.pdf?id=doi:10.1007/s00382-014-2241-2http://www.springerlink.com/content/fulltext.pdf?id=doi:10.1007/s00382-014-2241-2As the leading mode of the global atmospheric mass inter-annual variability, the Southern Hemisphere annular mode (SAM) may exert potential influences to the Northern Hemisphere (NH) climate, but the related physical mechanism is not yet clear. In this study, it is found that the November ecember (ND) SAM exhibits a significant inverse relationship with the winter precipitation over East Asia, particularly southern China. Observational and numerical evidences show that anomalous ND SAM is usually associated with a South Atlanticacific dipole sea surface temperature anomaly (SSTA) which persists into ensuring winter. The dipole SSTA can modulate the variability of the Inter-tropical Convergence Zone (ITCZ) in Pacific. Subsequently, a distinguished atmospheric tele-connection pattern is induced and prevails over the NH mid-latitude region as a response to the anomalous ITCZ. Large areas of high pressure anomalies are triggered at upper troposphere over East Asia and centered over southern China, which favors less precipitation over East Asia, particularly southern China, and vice versa. Through such a physical mechanism, the notable influence of the ND SAM can sustain through the following season and impact on the NH winter climate.
Zheng F., J. P. Li, 2012: Impact of preceding boreal winter southern hemisphere annular mode on spring precipitation over south China and related mechanism. Chinese Journal of Geophysics,55(11), 3542-3557, doi: 10.6038/j.issn.0001-5733. (in Chinese)10.6038/j.issn.0001-5733.2012.11.0043e448884-28ba-4ac5-97bd-1b48e9403ac1d41dde445d209b554a9d1565ddac00e7http%3A%2F%2Fen.cnki.com.cn%2FArticle_en%2FCJFDTOTAL-DQWX201211005.htmrefpaperuri:(78de27b6bced279cb62e2790407ca946)http://en.cnki.com.cn/Article_en/CJFDTOTAL-DQWX201211005.htmThe impact of the preceding boreal winter(December-February) Southern Hemisphere Annular Mode(SAM) on spring(March-May) rainfall over South China(RSC) and related physical mechanism were examined statistically by methods such as correlation analysis,composite analysis,singular value decomposition(SVD) and numerical simulation.The results show that there is a significant negative correlation relationship between the preceding winter SAM and spring RSC.That is,winters with strong(weak) SAM are often followed by less(more) RSC.In order to understand the physical mechanism of this relationship between signals from Southern Hemisphere mid-high latitudes and RSC in the following season,the role of ocean as underlying surface was investigated.It was found by diagnostic analyzing that in winters with strong SAM,latent heat fluxes change because of the change in sea surface wind speed,thus leading to positive(negative) SSTA in 30°S—45°S(45°—70°S).Because of large heat capacity of the ocean,the SSTA pattern persists to the following spring.Results from diagnostic analysis show that these SSTA lead to a series of consequence: Northwestern Pacific subtropical high weakens and the ridge extends less to west than normal years;an abnormal cyclonic circulation exists over West Pacific region;South China(SC) is controlled by abnormal northeast wind and wind divergence;water vapor transport to SC weakens,all these conditions lead to less RSC.The circulation anomalies related with SSTA caused by weak SAM are reversed,thus leading to more RSC.SST sensibility experiments carried out by CAM3 further certify above-mentioned circulation anomalies caused by SSTA.Results show that SSTA related with strong SAM lead to abnormal northeast wind,wind divergence,sinking movement over SC,thus leading to less RSC.In short,the winter SAM can impact the following spring RSC through SSTA in middle and high latitude in Southern Hemisphere,a manifestation of "ocean-atmosphere coupled bridge".The results imply that preceding winter SAM provides a significative prophase signature for forecasting spring RSC.
Zhu Y. L., 2012: Variations of the summer Somali and Australia cross-equatorial flows and the implications for the Asian summer monsoon. Adv. Atmos. Sci.,29(3), 509-518, doi: 10.1007/s00376-011-1120-6.10.1007/s00376-011-1120-6d68b04f4-6010-4873-83bc-1cdf3695ef661594f6d7518415d8833d7f16c5c61879http%3A%2F%2Fwww.springerlink.com%2Fopenurl.asp%3Fid%3Ddoi%3A10.1007%2Fs00376-011-1120-6refpaperuri:(354364416423c5130fcd25777269772a)http://d.wanfangdata.com.cn/Periodical_dqkxjz-e201203009.aspxThe temporal variations during 1948-2010 and vertical structures of the summer Somali and Australia cross-equatorial flows (CEFs) and the implications for the Asian summer monsoon were explored in this study.The strongest southerly and northerly CEFs exist at 925 hPa and 150 hPa level,respectively.The low-level Somali (LLS) CEFs were significantly connected with the rainfall in most regions of India (especially the monsoon regions),except in a small area in southwest India.In comparison to the climatology,the lowlevel Australia (LLA) CEFs exhibited stronger variations at interannual time scale and are more closely connected to the East Asian summer monsoon circulation than to the LLS CEFs.The East Asian summer monsoon circulation anomalies related to stronger LLA CEFs were associated with less water vapor content and less rainfall in the region between the middle Yellow River and Yangtze River and with more water vapor and more rainfall in southern China.The sea-surface temperature anomalies east of Australia related to summer LLA CEFs emerge in spring and persist into summer,with implications for the seasonal prediction of summer rainfall in East Asia.The connection between the LLA CEFs and East Asian summer monsoon rainfall may be partly due to its linkage with El Nino-Southern Oscillation.In addition,both the LLA and LLS CEFs exhibited interdecadal shifts in the late 1970s and the late 1990s,consistent with the phase shifts of Pacific Decadal Oscillation (PDO).