An S.-I., Y.-G. Ham, J.-S. Kug, F.-F. Jin, and I.-S. Kang, 2005: El Niño-La Niña asymmetry in the Coupled Model Intercomparison Project simulations. J.Climate, 18, 2617- 2627.
Adler, R. F., Coauthors, 2003: The version-2 Global Precipitation Climatology Project (GPCP) monthly precipitation analysis (1979-present). Journal of Hydrometeorology, 4( 6), 1147- 1167.10.1175/1525-7541(2003)004<1147:TVGPCP>2.0.CO;2e8c3bc43-a3c3-4a4f-a879-0056190f82f453064fd724346e9bd7d78eab17550121http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F23837598_The_Version_2_Global_Precipitation_Climatology_Project_%28GPCP%29_Monthly_Precipitation_Analysis_%281979-Present%29refpaperuri:(6d3afea98ce646aaa127cb18ee109d24)http://www.researchgate.net/publication/23837598_The_Version_2_Global_Precipitation_Climatology_Project_(GPCP)_Monthly_Precipitation_Analysis_(1979-Present)The Global Precipitation Climatology Project (GPCP) Version-2 Monthly Precipitation Analysis is described. This globally complete, monthly analysis of surface precipitation at 2.517 latitude 17 2.517 longitude resolution is available from January 1979 to the present. It is a merged analysis that incorporates precipitation estimates from low-orbit satellite microwave data, geosynchronous-orbit satellite infrared data, and surface rain gauge observations. The merging approach utilizes the higher accuracy of the low-orbit microwave observations to calibrate, or adjust, the more frequent geosynchronous infrared observations. The dataset is extended back into the premicrowave era (before mid-1987) by using infrared-only observations calibrated to the microwave-based analysis of the later years. The combined satellite-based product is adjusted by the rain gauge analysis. The dataset archive also contains the individual input fields, a combined satellite estimate, and error estimates for each field. This monthly analysis is the foundation for the GPCP suite of products, including those at finer temporal resolution. The 23-yr GPCP climatology is characterized, along with time and space variations of precipitation.
An S.-I., 2009: A review of interdecadal changes in the nonlinearity of the El Niño-Southern Oscillation. Theor. Appl. Climatol., 97, 29- 40.
An S.-I., F. F. Jin, 2004: Nonlinearity and asymmetry of ENSO. J.Climate, 17, 2399- 2412.10.1175/1520-0442(2004)017<2399:NAAOE>2.0.CO;2a37421263fc8dbde1ba16a6b544f8dc7http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F247769250_Nonlinearity_and_asymmetry_of_ENSOhttp://www.researchgate.net/publication/247769250_Nonlinearity_and_asymmetry_of_ENSOABSTRACT El Ni&ntilde;o events (warm) are often stronger than La Ni&ntilde;a events (cold). This asymmetry is an intrinsic nonlinear characteristic of the El Ni&ntilde;o-Southern Oscillation (ENSO) phenomenon. In order to measure the nonlinearity of ENSO, the maximum potential intensity (MPI) index and the nonlinear dynamic heating (NDH) of ENSO are proposed as qualitative and quantitative measures. The 1997/98 El Ni&ntilde;o that was recorded as the strongest event in the past century and another strong El Nino event in 1982/83 nearly reached the MPI. During these superwarming events, the normal climatological conditions of the ocean and atmosphere were collapsed completely. The huge bursts of ENSO activity manifested in these events are attributable to the nonlinear dynamic processes. Through a heat budget analysis of the ocean mixed layer it is found that throughout much of the ENSO episodes of 1982/83 and 1997/98, the DH strengthened these warm events and weakened subsequent La Nina events. This led to the warm-cold asymmetry. It is also found that the eastward-propagating feature in these two El Ni&ntilde;o events provided a favorable phase relationship between temperature and current that resulted in the strong nonlinear dynamical warming. For the westward-propagating El Nino events prior to the late 1970s (e.g., 1957/58 and 1972/73 ENSOs) the phase relationships between zonal temperature gradient and current and between the surface and subsurface temperature anomalies are unfavorable for nonlinear dynamic heating, and thereby the ENSO events are not strong.
An S.-I., Y.-G. Ham, J.-S. Kug, F. F. Jin, and I.-S. Kang, 2009: El Niño-La Niña asymmetry in the coupled model intercomparison project simulations. J.Climate, 18, 2617- 2627.
Bjerknes J., 1969: Atmospheric teleconnections from the equatorial Pacific. Mon. Wea. Rev., 97, 163- 172.10.1175/1520-0493(1969)0972.3.CO;296e8f63f-f22c-4793-816c-0525274d0af3d99667c470b8e221952789ed1bd6b4a7http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F243781719_Atmospheric_Teleconnections_from_the_Equatorial_PACIFIC1refpaperuri:(20704598911cca9eea64a71df5188422)http://www.researchgate.net/publication/243781719_Atmospheric_Teleconnections_from_the_Equatorial_PACIFIC1Abstract The “high index” response of the northeast Pacific westerlies to big positive anomalies of equatorial sea temperature, observed in the winter of 1957–58, has been found to repeat during the major equatorial sea temperature maxima in the winters of 1963–64 and 1965–66. The 1963 positive temperature anomaly started early enough to exert the analogous effect on the atmosphere of the south Indian Ocean during its winter season. The maxima of the sea temperature in the eastern and central equatorial Pacific occur as a result of anomalous weakening of the trade winds of the Southern Hemisphere with inherent weakening of the equatorial upwelling. These anomalies are shown to be closely tied to the “Southern Oscillation” of Sir Gilbert Walker.
Burgers G., D. B. Stephenson, 1999: The "Normality" of El Niño. Geophys. Res. Lett., 26, 1027- 1030.
Cai, W. J., Coauthors, 2014: Increasing frequency of extreme El Niño events due to greenhouse warming. Nature Clim.Change, 4, 111- 116.10.1038/nclimate2100769e1757-d3c5-44f4-8bf6-04b26f4295c4b86801d74f32d7deb277c1f76e82b0a7http%3A%2F%2Fwww.nature.com%2Fnclimate%2Fjournal%2Fv4%2Fn2%2Fnclimate2100%2Fmetricsrefpaperuri:(cefa9fea45a10bb29bb45723d32e2d38)http://www.nature.com/nclimate/journal/v4/n2/nclimate2100/metricsEl Niño events are a prominent feature of climate variability with global climatic impacts. The 1997/98 episode, often referred to as `the climate event of the twentieth century', and the 1982/83 extreme El Niño, featured a pronounced eastward extension of the west Pacific warm pool and development of atmospheric convection, and hence a huge rainfall increase, in the usually cold and dry equatorial eastern Pacific. Such a massive reorganization of atmospheric convection, which we define as an extreme El Niño, severely disrupted global weather patterns, affecting ecosystems, agriculture, tropical cyclones, drought, bushfires, floods and other extreme weather events worldwide. Potential future changes in such extreme El Niño occurrences could have profound socio-economic consequences. Here we present climate modelling evidence for a doubling in the occurrences in the future in response to greenhouse warming. We estimate the change by aggregating results from climate models in the Coupled Model Intercomparison Project phases 3 (CMIP3; ref. ) and 5 (CMIP5; ref. ) multi-model databases, and a perturbed physics ensemble. The increased frequency arises from a projected surface warming over the eastern equatorial Pacific that occurs faster than in the surrounding ocean waters, facilitating more occurrences of atmospheric convection in the eastern equatorial region.
Cane M. A., 1983: Oceanographic events during El Niño. Science, 222, 1189- 1195.
Carton J. A., B. S. Giese, 2008: A reanalysis of ocean climate using Simple Ocean Data Assimilation (SODA). Mon. Wea. Rev.,136, 2999-3017, doi: 10.1175/2007MWR1978.1.10.1175/2007MWR1978.1454a78caf21a0c20ffebed73838f4b6ahttp%3A%2F%2Fwww.researchgate.net%2Fpublication%2F252645984_A_Reanalysis_of_Ocean_Climate_Using_Simple_Ocean_Data_Assimilation_%28SODA%29http://www.researchgate.net/publication/252645984_A_Reanalysis_of_Ocean_Climate_Using_Simple_Ocean_Data_Assimilation_(SODA)Abstract This paper describes the Simple Ocean Data Assimilation (SODA) reanalysis of ocean climate variability. In the assimilation, a model forecast produced by an ocean general circulation model with an average resolution of 0.25° × 0.4° × 40 levels is continuously corrected by contemporaneous observations with corrections estimated every 10 days. The basic reanalysis, SODA 1.4.2, spans the 44-yr period from 1958 to 2001, which complements the span of the 40-yr European Centre for Medium-Range Weather Forecasts (ECMWF) atmospheric reanalysis (ERA-40). The observation set for this experiment includes the historical archive of hydrographic profiles supplemented by ship intake measurements, moored hydrographic observations, and remotely sensed SST. A parallel run, SODA 1.4.0, is forced with identical surface boundary conditions, but without data assimilation. The new reanalysis represents a significant improvement over a previously published version of the SODA algorithm. In particular, eddy kinetic energy and sea level variability are much larger than in previous versions and are more similar to estimates from independent observations. One issue addressed in this paper is the relative importance of the model forecast versus the observations for the analysis. The results show that at near-annual frequencies the forecast model has a strong influence, whereas at decadal frequencies the observations become increasingly dominant in the analysis. As a consequence, interannual variability in SODA 1.4.2 closely resembles interannual variability in SODA 1.4.0. However, decadal anomalies of the 0–700-m heat content from SODA 1.4.2 more closely resemble heat content anomalies based on observations.
Graham N. E., T. P. Barnett, 1987: Sea surface temperature, surface wind divergence, and convection over tropical oceans. Science, 238, 657- 659.10.1126/science.238.4827.6571781654341e26ab56c79ce0b03a7e4fae6aa53e1http%3A%2F%2Fmed.wanfangdata.com.cn%2FPaper%2FDetail%2FPeriodicalPaper_PM17816543http://med.wanfangdata.com.cn/Paper/Detail/PeriodicalPaper_PM17816543Large-scale convection over the warm tropical oceans provides an important portion of the driving energy for the general circulation of the atmosphere. Analysis of regional associations between ocean temperature, surface wind divergence, and convection produced two important results. First, over broad regions of the Indian and Pacific oceans, sea surface temperatures (SSTs) in excess of 27.5 degrees C are required for large-scale deep convection to occur. However, SSTs above that temperature are not a sufficient condition for convection and further increases in SST appear to have little effect on the intensity of convection. Second, when SSTs are above 27.5 degrees C, surface wind divergence is closely associated with the presence or absence of deep convection. Although this result could have been expected, it was also found that areas of persistent divergent surface flow coincide with regions where convection appears to be consistently suppressed even when SSTs are above 27.5 degrees C. Thus changes in atmospheric stability caused by remotely forced changes in subsidence aloft may play a major role in regulating convection over warm tropical oceans.
Guilyardi E., 2006: El Niño-mean state-seasonal cycle interactions in a multi-model ensemble. Climate Dyn., 26, 329- 348.10.1007/s00382-005-0084-68cfa8cce-3e1e-4ada-8abb-edd855773cbe06cb04425f8095f8b8462bc8dd782f4bhttp%3A%2F%2Fonlinelibrary.wiley.com%2Fresolve%2Freference%2FXREF%3Fid%3D10.1007%2Fs00382-005-0084-6refpaperuri:(4a81bcdb631b7c7b2b35c19af1602e34)http://onlinelibrary.wiley.com/resolve/reference/XREF?id=10.1007/s00382-005-0084-6The modelled El Ni09o–mean state–seasonal cycle interactions in 23 coupled ocean–atmosphere GCMs, including the recent IPCC AR4 models, are assessed and compared to observations and theory. The models show a clear improvement over previous generations in simulating the tropical Pacific climatology. Systematic biases still include too strong mean and seasonal cycle of trade winds. El Ni09o amplitude is shown to be an inverse function of the mean trade winds in agreement with the observed shift of 1976 and with theoretical studies. El Ni09o amplitude is further shown to be an inverse function of the relative strength of the seasonal cycle. When most of the energy is within the seasonal cycle, little is left for inter-annual signals and vice versa. An interannual coupling strength (ICS) is defined and its relation with the modelled El Ni09o frequency is compared to that predicted by theoretical models. An assessment of the modelled El Ni09o in term of SST mode (S-mode) or thermocline mode (T-mode) shows that most models are locked into a S-mode and that only a few models exhibit a hybrid mode, like in observations. It is concluded that several basic El Ni09o–mean state–seasonal cycle relationships proposed by either theory or analysis of observations seem to be reproduced by CGCMs. This is especially true for the amplitude of El Ni09o and is less clear for its frequency. Most of these relationships, first established for the pre-industrial control simulations, hold for the double and quadruple CO 2 stabilized scenarios. The models that exhibit the largest El Ni09o amplitude change in these greenhouse gas (GHG) increase scenarios are those that exhibit a mode change towards a T-mode (either from S-mode to hybrid or hybrid to T-mode). This follows the observed 1976 climate shift in the tropical Pacific, and supports the—still debated—finding of studies that associated this shift to increased GHGs. In many respects, these models are also among those that best simulate the tropical Pacific climatology (ECHAM5/MPI-OM, GFDL-CM2.0, GFDL-CM2.1, MRI-CGM2.3.2, UKMO-HadCM3). Results from this large subset of models suggest the likelihood of increased El Ni09o amplitude in a warmer climate, though there is considerable spread of El Ni09o behaviour among the models and the changes in the subsurface thermocline properties that may be important for El Ni09o change could not be assessed. There are no clear indications of an El Ni09o frequency change with increased GHG.
Ham Y. G., J. S. Kug, 2012: How well do current climate models simulate two types of El Niño? Climate Dyn., 39, 383- 398.
Ham Y. G., J. S. Kug, 2014: Improvement of ENSO simulation based on intermodel diversity? J. Climate., 28, 998- 1015.10.1175/JCLI-D-14-00376.19597fe22-f238-4291-9b80-8c3bbc188aec4d905a10d7e0fdcca181bc7975ac0ce4http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F272403202_Improvement_of_ENSO_Simulation_Based_on_Intermodel_Diversityrefpaperuri:(bb9b62e1fef225d77f231ab2eee72972)http://www.researchgate.net/publication/272403202_Improvement_of_ENSO_Simulation_Based_on_Intermodel_DiversityAbstract In this study, a new methodology is developed to improve the climate simulation of state-of-the-art coupled global climate models (GCMs), by a postprocessing based on the intermodel diversity. Based on the close connection between the interannual variability and climatological states, the distinctive relation between the intermodel diversity of the interannual variability and that of the basic state is found. Based on this relation, the simulated interannual variabilities can be improved, by correcting their climatological bias. To test this methodology, the dominant intermodel difference in precipitation responses during El Ni09o–Southern Oscillation (ENSO) is investigated, and its relationship with climatological state. It is found that the dominant intermodel diversity of the ENSO precipitation in phase 5 of the Coupled Model Intercomparison Project (CMIP5) is associated with the zonal shift of the positive precipitation center during El Ni09o. This dominant intermodel difference is significantly correlated with the basic states. The models with wetter (dryer) climatology than the climatology of the multimodel ensemble (MME) over the central Pacific tend to shift positive ENSO precipitation anomalies to the east (west). Based on the model’s systematic errors in atmospheric ENSO response and bias, the models with better climatological state tend to simulate more realistic atmospheric ENSO responses. Therefore, the statistical method to correct the ENSO response mostly improves the ENSO response. After the statistical correction, simulating quality of the MME ENSO precipitation is distinctively improved. These results provide a possibility that the present methodology can be also applied to improving climate projection and seasonal climate prediction.
Harrison D. E., G. A. Vecchi, 1999: On the termination of El Niño. Geophys. Res. Lett., 26, 1593- 1596.
Jin F. F., D. Neelin, and M. Ghil, 1994: El Niño on the devil's staircase: Annual subharmonic steps to chaos. Science, 264, 70- 72.10.1126/science.264.5155.7017778135e5b8ea85-fea8-4ca7-885c-11b975eb314f98e80aa2e7f58834110fd253a7264d36http%3A%2F%2Fmed.wanfangdata.com.cn%2FPaper%2FDetail%2FPeriodicalPaper_PM17778135refpaperuri:(49aff9c3bdf7d6d23d26fbb73d1eb8d1)http://med.wanfangdata.com.cn/Paper/Detail/PeriodicalPaper_PM17778135The source of irregularity in El Ni09o, the large interannual climate variation of the Pacific ocean-atmosphere system, has remained elusive. Results from an El Ni09o model exhibit transition to chaos through a series of frequency-locked steps created by nonlinear resonance with the Earth's annual cycle. The overlapping of these resonances leads to the chaotic behavior. This transition scenario explains a number of climate model results and produces spectral characteristics consistent with currently available data.
Jin F. F., S.-I. An, A. Timmermann, and J. X. Zhao, 2003: Strong El Niño events and nonlinear dynamical heating. Geophys. Res. Lett., 30,1120, doi: 10.1029/2002GL016356.10.1029/2002GL0163562a3fe30b-9f5d-402e-bd58-dd751d022f88283ae845ab50464b618f67270e65fcd5http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2002GL016356%2Fcitedbyrefpaperuri:(815eea14e0c448cbdbd39c7519a24bf0)http://onlinelibrary.wiley.com/doi/10.1029/2002GL016356/citedby[1] We present evidence showing that the nonlinear dynamic heating (NDH) in the tropical Pacific ocean heat budget is essential in the generation of intense El Ni09o events as well as the observed asymmetry between El Ni09o (warm) and La Ni09a (cold) events. The increase in NDH associated with the enhanced El Ni09o activity had an influence on the recent tropical Pacific warming trend and it might provide a positive feedback mechanism for climate change in the tropical Pacific.
Kim S. T., J. Y. Yu, 2012: The two types of ENSO in CMIP5 models. Geophys. Res. Lett., 39,L11704, doi: 10.1029/2012 GL052006.10.1029/2012GL052006b4418360ec3a2a6a6025d2d82813920bhttp%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2012GL052006%2Ffullhttp://onlinelibrary.wiley.com/doi/10.1029/2012GL052006/full[1] In this study, we evaluate the intensity of the Central-Pacific (CP) and Eastern-Pacific (EP) types of El Niño-Southern Oscillation (ENSO) simulated in the pre-industrial, historical, and the Representative Concentration Pathways (RCP) 4.5 experiments of the Coupled Model Intercomparison Project Phase 5 (CMIP5). Compared to the CMIP3 models, the pre-industrial simulations of the CMIP5 models are found to (1) better simulate the observed spatial patterns of the two types of ENSO and (2) have a significantly smaller inter-model diversity in ENSO intensities. The decrease in the CMIP5 model discrepancies is particularly obvious in the simulation of the EP ENSO intensity, although it is still more difficult for the models to reproduce the observed EP ENSO intensity than the observed CP ENSO intensity. Ensemble means of the CMIP5 models indicate that the intensity of the CP ENSO increases steadily from the pre-industrial to the historical and the RCP4.5 simulations, but the intensity of the EP ENSO increases from the pre-industrial to the historical simulations and then decreases in the RCP4.5 projections. The CP-to-EP ENSO intensity ratio, as a result, is almost the same in the pre-industrial and historical simulations but increases in the RCP4.5 simulation.
Kim S. T., W. J. Cai, F. F. Jin, J. Y. Yu.2014: ENSO stability in coupled climate models and its association with mean state. Climate Dyn., 42, 3313- 3321.10.1007/s00382-013-1833-62a973cc65405449ee31a0f119381aab3http%3A%2F%2Flink.springer.com%2F10.1007%2Fs00382-013-1833-6http://link.springer.com/10.1007/s00382-013-1833-6In this study, using the Bjerknes stability (BJ) index analysis, we estimate the overall linear El Nino-Southern Oscillation (ENSO) stability and the relative contribution of positive feedbacks and damping processes to the stability in historical simulations of Coupled Model Intercomparison Project Phase 5 (CMIP5) models. When compared with CMIP3 models, the ENSO amplitudes and the ENSO stability as estimated by the BJ index in the CMIP5 models are more converged around the observed, estimated from the atmosphere and ocean reanalysis data sets. The reduced diversity among models in the simulated ENSO stability can be partly attributed to the reduced spread of the thermocline feedback and Ekman feedback terms among the models. However, a systematic bias persists from CMIP3 to CMIP5. In other words, the majority of the CMIP5 models analyzed in this study still underestimate the zonal advective feedback, thermocline feedback and thermodynamic damping terms, when compared with those estimated from reanalysis. This discrepancy turns out to be related with a cold tongue bias in coupled models that causes a weaker atmospheric thermodynamical response to sea surface temperature changes and a weaker oceanic response (zonal currents and zonal thermocline slope) to wind changes.
Kug J.-S., I.-S. Kang, and S.-I. An, 2003: Symmetric and antisymmetric mass exchanges between the equatorial and off-equatorial Pacific associated with ENSO. J. Geophys. Res., 108, 3284.10.1029/2002JC0016716c13226569fe457543492ca51bf4d8e7http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2002JC001671%2Ffullhttp://onlinelibrary.wiley.com/doi/10.1029/2002JC001671/fullAbstract Top of page Abstract 1.Introduction 2.Ocean Assimilation Data Analysis 3.Simple Theoretical Model 4.Intermediate Model Experiments 5.Summary and Discussions AppendixA Acknowledgments References [1] Mass exchanges in the upper ocean between the equatorial and off-equatorial Pacific Ocean associated with the El Niño/Southern Oscillation (ENSO) are investigated using the National Centers for Environmental Prediction (NCEP) ocean assimilation data. The data show that ENSO-related meridional mass transport in the Northern Hemisphere (NH) is larger than that in the Southern Hemisphere (SH). We found that the antisymmetric characteristics are mainly due to a southward shift of the maximum zonal wind stress anomaly during the ENSO mature phase. The Ekman and geostrophic transports associated with ENSO are separated into symmetric and antisymmetric components. For the symmetric part, the mass divergence over the equatorial Pacific by the geostrophic transport is generally larger than the convergence by the Ekman transport during the El Niño mature phase. Therefore mass is transported from the equator to off the equator at this time. As for the antisymmetric part, the Ekman transport due to antisymmetric wind stress dominates the geostrophic transport so that the mass is transported from the SH to the NH during the El Niño mature phase. The net mass transport in the NH is larger than that in the SH. A theoretical interpretation and intermediate model experiments support these arguments.
Kug J.-S., F.-F. Jin, and S.-I. An, 2009: Two-types of El Niño events: Cold tongue El Niño and warm pool El Niño. J.Climate, 22, 1499- 1515.
Latif M., Coauthors, 2001: ENSIP: The El Niño simulation intercomparison project. Climate Dyn., 18, 255- 276.c18680b6-7af8-4c2e-8c2b-9d20a9b65bd44981b66ffba4a1c8d12a3bad5a3566b1http%3A%2F%2Flink.springer.com%2F10.1007%252Fs003820100174refpaperuri:(71ef3dead411f9ec8190aa51b0a35d33)/s?wd=paperuri%3A%2871ef3dead411f9ec8190aa51b0a35d33%29&filter=sc_long_sign&tn=SE_xueshusource_2kduw22v&sc_vurl=http%3A%2F%2Flink.springer.com%2F10.1007%252Fs003820100174&ie=utf-8
Leloup J., M. Lengaigne, and J.-P. Boulanger, 2008: Twentieth century ENSO characteristics in the IPCC database. Climate Dyn., 30, 277- 291.10.1007/s00382-007-0284-3cbcbde8c566ee6f687ec1de73e499be8http%3A%2F%2Flink.springer.com%2Farticle%2F10.1007%2Fs00382-007-0284-3http://link.springer.com/article/10.1007/s00382-007-0284-3In this paper, we assess and compare to observations the spatial characteristics of the twentieth Century ENSO SST variability simulated by 23 models of the IPCC-AR4/CMIP3 database. The analysis is confined to the SST anomalies along the equatorial Pacific and is based on the use of a non-linear neural classification algorithm, the Self-Organizing Maps. Systematic biases include a larger than observed proportion for modelled ENSO maximum variability occurring in the Western Pacific. No clear relationship is found between this bias and the characteristics of the modelled mean state bias in the equatorial Pacific. This bias is mainly related to a misrepresentation of both El Ni01±o and La Ni01±a termination phases for most of the models. In contrast, the onset phase is quite well simulated. Modelled El Ni01±o and La Ni01±a peak phases display an asymmetric bias. Whereas the main bias of the modelled El Ni01±o peak is to exhibit a maximum in the western Pacific, the simulated La Ni01±a bias mainly occurs in the central Pacific. In addition, some models are able to capture the observed El Ni01±o peak characteristics while none of them realistically simulate La Ni01±a peaks. It also arises that the models closest to the observations score unevenly in reproducing the different phases, preventing an accurate classification of the models quality to reproduce the overall ENSO-like variability.
Li G., S. P. Xie, 2012: Origins of tropical-wide SST biases in CMIP multi-model ensembles. Geophys. Res. Lett., 39,L22703, doi: 10.1029/2012GL053777.10.1029/2012GL053777280febdcca368b60fb64d5f918b24696http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2012GL053777%2Fcitedbyhttp://onlinelibrary.wiley.com/doi/10.1029/2012GL053777/citedbyABSTRACT Long-standing simulation errors limit the utility of climate models. Overlooked are tropical-wide errors, with sea surface temperature (SST) biasing high or low across all the tropical ocean basins. Our analysis based on Coupled Model Intercomparison Project (CMIP) multi-model ensembles shows that such SST biases can be classified into two types: one with a broad meridional structure and of the same sign across all basins that is highly correlated with the tropical mean; and one with large inter-model variability in the cold tongues of the equatorial Pacific and Atlantic. The first type can be traced back to biases in atmospheric simulations of cloud cover, with cloudy models biasing low in tropical-wide SST. The second type originates from the diversity among models in representing the thermocline depth; models with a deep thermocline feature a warm cold tongue on the equator. Implications for inter-model variability in precipitation climatology and SST threshold for convection are discussed.
Li G., S. P. Xie, 2014: Tropical biases in CMIP5 multimodel ensemble: The excessive equatorial pacific cold tongue and double ITCZ problems. J. Climate,27, 1765-1780, doi: 10.1175/JCLI-D-13-00337.110.1175/JCLI-D-13-00337.1e5394ffcc15468747f6408a03a9d234dhttp%3A%2F%2Fwww.researchgate.net%2Fpublication%2F263051516_Tropical_Biases_in_CMIP5_Multimodel_Ensemble_The_Excessive_Equatorial_Pacific_Cold_Tongue_and_Double_ITCZ_Problems%2A%3Fev%3Dauth_pubhttp://www.researchgate.net/publication/263051516_Tropical_Biases_in_CMIP5_Multimodel_Ensemble_The_Excessive_Equatorial_Pacific_Cold_Tongue_and_Double_ITCZ_Problems*?ev=auth_pubAbstract Errors of coupled general circulation models (CGCMs) limit their utility for climate prediction and projection. Origins of and feedback for tropical biases are investigated in the historical climate simulations of 18 CGCMs from phase 5 of the Coupled Model Intercomparison Project (CMIP5), together with the available Atmospheric Model Intercomparison Project (AMIP) simulations. Based on an intermodel empirical orthogonal function (EOF) analysis of tropical Pacific precipitation, the excessive equatorial Pacific cold tongue and double intertropical convergence zone (ITCZ) stand out as the most prominent errors of the current generation of CGCMs. The comparison of CMIP–AMIP pairs enables us to identify whether a given type of errors originates from atmospheric models. The equatorial Pacific cold tongue bias is associated with deficient precipitation and surface easterly wind biases in the western half of the basin in CGCMs, but these errors are absent in atmosphere-only models, indicating that the errors arise from the interaction with the ocean via Bjerknes feedback. For the double ITCZ problem, excessive precipitation south of the equator correlates well with excessive downward solar radiation in the Southern Hemisphere (SH) midlatitudes, an error traced back to atmospheric model simulations of cloud during austral spring and summer. This extratropical forcing of the ITCZ displacements is mediated by tropical ocean–atmosphere interaction and is consistent with recent studies of ocean–atmospheric energy transport balance.
McGregor S., A. Timmermann, N. Schneider, M. Stuecker, and M. England, 2012: The Effect of the South Pacific convergence zone on the termination of El Niño events and the meridional asymmetry of ENSO. J. Climate,25, 5566-5586, doi: 10.1175/JCLI-D-11-00332.1.10.1175/JCLI-D-11-00332.1de127213-bfde-48ad-b8c0-84466c5291cf2c63e8f4b8a110eab9cb29a5740b75fdhttp%3A%2F%2Fwww.researchgate.net%2Fpublication%2F258201135_The_Effect_of_the_South_Pacific_Convergence_Zone_on_the_Termination_of_El_Nino_Events_and_the_Meridional_Asymmetry_of_ENSOrefpaperuri:(be83c1e3d61b474e013c47898a83b8fb)http://www.researchgate.net/publication/258201135_The_Effect_of_the_South_Pacific_Convergence_Zone_on_the_Termination_of_El_Nino_Events_and_the_Meridional_Asymmetry_of_ENSODuring large El Ni01±o events the westerly wind response to the eastern equatorial Pacific sea surface temperature anomalies (SSTAs) shifts southward during boreal winter and early spring, reaching latitudes of 500°-700°S. The resulting meridional asymmetry, along with a related seasonal weakening of wind anomalies on the equator are key elements in the termination of strong El Ni01±o events. Using an intermediate complexity atmosphere model it is demonstrated that these features result from a weakening of the climatological wind speeds south of the equator toward the end of the calendar year. The reduced climatological wind speeds, which are associated with the seasonal intensification of the South Pacific convergence zone (SPCZ), lead to anomalous boundary layer Ekman pumping and a reduced surface momentum damping of the combined boundary layer/lower-troposphere surface wind response to El Ni01±o. This allows the associated zonal wind anomalies to shift south of the equator. Furthermore, using a linear shallow-water ocean model it is demonstrated that this southward wind shift plays a prominent role in changing zonal mean equatorial heat content and is solely responsible for establishing the meridional asymmetry of thermocline depth in the turnaround (recharge/discharge) phase of ENSO. This result calls into question the sole role of oceanic Rossby waves in the phase synchronized termination of El Ni01±o events and suggests that the development of a realistic climatological SPCZ in December-February/March-May (DJF/MAM) is one of the key factors in the seasonal termination of strong El Ni01±o events.
McGregor S., N. Ramesh, P. Spence, M. H. England , M. J. McPhaden, and A. Santoso, 2013: Meridional movement of wind anomalies during ENSO events and their role in event termination. Geophys. Res. Lett., 40, 749- 754.10.1002/grl.501363977f4b7-6818-4e97-878e-46c114f48f7c02a6aeed696b1f5ba978b637bbb537c7http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1002%2Fgrl.50136%2Fabstractrefpaperuri:(0cc5dacd0eb9feb5669099e48c196269)http://onlinelibrary.wiley.com/doi/10.1002/grl.50136/abstract[1] Observational analysis has shown that when El Ni&ntilde;o-Southern Oscillation (ENSO) events typically reach their peak amplitude in boreal winter, the associated zonal wind anomalies abruptly shift southward so that the maximum anomalous zonal wind is located around 5&ndash;7S. Here, an analysis utilizing multiple wind products identifies a clear ENSO phase nonlinearity in the extent of this meridional wind movement and its dynamically linked changes in equatorial heat content. It is shown that the meridional wind movement and its discharging effect increase with increasing El Ni&ntilde;o amplitude, while both remain relatively small regardless of La Ni&ntilde;a amplitude. This result implies that asymmetries in the extent of the meridional wind shift may contribute to the observed asymmetry in the duration of El Ni&ntilde;o and La Ni&ntilde;a events. We also evaluate the result sensitivities to wind product selection and discuss Eastern Pacific (EP) and Central Pacific (CP) El Ni&ntilde;o event differences.
Mechoso C.R., Coauthors, 1995: The seasonal cycle over the tropical Pacific in coupled ocean-atmosphere general circulation models. Mon. Wea. Rev., 123, 2825- 2838.a8a062c1-c3d7-4ffc-93fa-d23d412d1cf99f673a672cd7911c72d6a7811d47a333http%3A%2F%2Feuropepmc.org%2Fabstract%2FMED%2F25279012refpaperuri:(b95ef30e2e6318335f8488a917ddf578)/s?wd=paperuri%3A%28b95ef30e2e6318335f8488a917ddf578%29&filter=sc_long_sign&tn=SE_xueshusource_2kduw22v&sc_vurl=http%3A%2F%2Feuropepmc.org%2Fabstract%2FMED%2F25279012&ie=utf-8
Philand er, S. G. H., 1983: El Niño Southern Oscillation phenomena. Nature, 302, 295- 301.10.1038/302295a09c624f8d-3d06-4fb8-86ae-062bf759e857af1fff3ee8e054a7551b7a051f87d785http://www.researchgate.net/publication/258931230_El_Nio_Southern_Oscillation_phenomenahttp://www.researchgate.net/publication/258931230_El_Nio_Southern_Oscillation_phenomenaAt intervals that vary from 2 to 10 yr sea-surface temperatures and rainfall are unusually high and the tradewinds are unusually weak over the tropical Pacific Ocean. These Southern Oscillation El Niño events which devastate the ecology of the coastal zones of Ecuador and Peru, which affect the global atmospheric circulation and which can contribute to severe winters over northern America, often develop in a remarkably predictable manner. But the event which began in 1982 has not followed this pattern.
Rayner N. A., D. E. Parker, E. B. Horton, C. K. Folland, L. V. Alexander, D. P. Rowell, E. C. Kent, and A. Kaplan2003: Global analyses of sea surface temperature, sea ice, and night marine air temperature since the late nineteenth century, J. Geophys. Res., 108,4407, doi: 10.1029/2002JD002670.10.1029/2002JD0026700831f099871c89699f00bb6e2586346bhttp%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2002JD002670%2Ffullhttp://onlinelibrary.wiley.com/doi/10.1029/2002JD002670/full[1] We present the Met Office Hadley Centre's sea ice and sea surface temperature (SST) data set, HadISST1, and the nighttime marine air temperature (NMAT) data set, HadMAT1. HadISST1 replaces the global sea ice and sea surface temperature (GISST) data sets and is a unique combination of monthly globally complete fields of SST and sea ice concentration on a 1 latitude-longitude grid from 1871. The companion HadMAT1 runs monthly from 1856 on a 5 latitude-longitude grid and incorporates new corrections for the effect on NMAT of increasing deck (and hence measurement) heights. HadISST1 and HadMAT1 temperatures are reconstructed using a two-stage reduced-space optimal interpolation procedure, followed by superposition of quality-improved gridded observations onto the reconstructions to restore local detail. The
Rodgers K. B., P. Friederichs, and M. Latif, 2004: Tropical Pacific decadal variability and its relation to decadal modulations of ENSO. J.Climate, 17, 3761- 3774.10.1175/1520-0442(2004)0172.0.CO;2118ffde9f8a48c6b13976c97af77ff17http%3A%2F%2Fwww.researchgate.net%2Fpublication%2F249611486_Tropical_Pacific_Decadal_Variability_and_Its_Relation_to_Decadal_Modulations_of_ENSOhttp://www.researchgate.net/publication/249611486_Tropical_Pacific_Decadal_Variability_and_Its_Relation_to_Decadal_Modulations_of_ENSOAbstract A 1000-yr integration of a coupled ocean–atmosphere model (ECHO-G) has been analyzed to describe decadal to multidecadal variability in equatorial Pacific sea surface temperature (SST) and thermocline depth (Z20), and their relationship to decadal modulations of El Ni09o–Southern Oscillation (ENSO) behavior. Although the coupled model is characterized by an unrealistically regular 2-yr ENSO period, it exhibits significant modulations of ENSO amplitude on decadal to multidecadal time scales. The authors' main finding is that the structures in SST and Z20 characteristic of tropical Pacific decadal variability (TPDV) in the model are due to an asymmetry between the anomaly patterns associated with the model's El Ni09o and La Ni09a states, with this asymmetry reflecting a nonlinearity in ENSO variability. As a result, the residual (i.e., the sum) of the composite El Ni09o and La Ni09a patterns exhibits a nonzero dipole structure across the equatorial Pacific, with positive perturbation values in the east and negative values in the west for SST and Z20. During periods when ENSO variability is strong, this difference manifests itself as a rectified change in the mean state. For comparison, a similar analysis was applied to a gridded SST dataset spanning the period 1871–1999. The data confirms that the asymmetry between the SST anomaly patterns associated with El Ni09o and La Ni09a for the model is realistic. However, ENSO in the observations is weaker and not as regular as in the model, and thus the changes due to ENSO asymmetries for the observations can only be detected in the Ni09o-12 region.
Sun D. Z., T. Zhang, 2006: A regulatory effect of ENSO on the time-mean thermal stratification of the equatorial upper ocean. Geophys. Res. Lett., 33,L07710, doi: 10.1029/2005 GL025296.10.1029/2005GL0252961a21377cc42fe1d580647c8d97b26875http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2005GL025296%2Fcitedbyhttp://onlinelibrary.wiley.com/doi/10.1029/2005GL025296/citedby[1] To investigate the role of ENSO in regulating the time-mean thermal stratification of the equatorial Pacific, perturbation experiments are conducted in pairs with a coupled model. In one experiment, ENSO is turned off while in the other experiment ENSO is kept on. Perturbations are introduced through either enhancing tropical heating or increasing subtropical cooling. In the absence of ENSO, the time-mean difference between the warm-pool SST (Tw) and the characteristic temperature of the equatorial thermocline (Tc) responds sensitively to either enhanced tropical heating or enhanced subtropical cooling. In the presence of ENSO, such a sensitivity to destabilizing forcing disappears. The lack of sensitivity in the response of Tw-Tc is linked to a stronger ENSO in response to the destabilizing forcing. ENSO in the model acts as a basin-scale heat “mixer” that enables surface heat to be transported to the depths of the equatorial thermocline. The study raises the question whether models with poor simulations of ENSO can give reliable predictions of the response of the time-mean climate to global warming.
Sun D.-Z., Y. Yu, and T. Zhang2009: Tropical water vapor and cloud feedbacks in climate models: A further assessment using coupled simulations. J.Climate, 22( 5), 1287- 1304.10.1175/2008JCLI2267.1b325b978aa31e70c848ba07828f7fa04http%3A%2F%2Fonlinelibrary.wiley.com%2Fresolve%2Freference%2FADS%3Fid%3D2009JCli...22.1287Shttp://onlinelibrary.wiley.com/resolve/reference/ADS?id=2009JCli...22.1287SBy comparing the response of clouds and water vapor to ENSO forcing in nature with that in Atmospheric Model Intercomparison Project (AMIP) simulations by some leading climate models, an earlier evaluation of tropical cloud and water vapor feedbacks has revealed the following two common biases in the models: (1) an underestimate of the strength of the negative cloud albedo feedback and (2) an o...
Sun Y., D. Z. Sun, L. X. Wu, and F. Wang, 2013: Western Pacific warm pool and ENSO asymmetry in CMIP3 models. Adv. Atmos. Sci.,30, 940-953, doi: 10.1007/s00376-012-2161-1.10.1007/s00376-012-2161-1a3f1f366d76f90ccbc9e4be5672725e5http%3A%2F%2Flink.springer.com%2F10.1007%2Fs00376-012-2161-1http://d.wanfangdata.com.cn/Periodical_dqkxjz-e201303029.aspx
Wang B., S.-I. An, 2002: A mechanism for decadal changes of ENSO behavior: Roles of background wind changes. Climate Dyn., 18, 475- 486.10.1007/s00382-001-0189-56ae2277ebbc8928cd9583274ce9d4bd2http%3A%2F%2Fonlinelibrary.wiley.com%2Fresolve%2Freference%2FXREF%3Fid%3D10.1007%2Fs00382-001-0189-5http://onlinelibrary.wiley.com/resolve/reference/XREF?id=10.1007/s00382-001-0189-5This study explains why a number of El Nino properties (period, amplitude, structure, and propagation) have changed in a coherent manner since the late 1970s and why these changes had almost concurred with the Pacific decadal climate shift. Evidence is presented to show that from the pre-shift (1961-1975) to the post-shift (1981-1995) epoch, significant changes in the tropical Pacific are found in the surface winds and temperature, whereas changes in the thermocline are uncertain. Numerical experiments with the Cane and Zebiak model demonstrate that the decadal changes in the surface winds qualitatively reproduce the observed coherent changes in El Nino properties. The fundamental factor that altered the model's El Nino is the decadal changes of the background equatorial winds and associated upwelling. The annual cycle is also necessary for the mean state to modulate El Nino. From the pre- to post-shift epoch, the changes in the background winds and upwelling modify the structure of the coupled mode (eastward displacement of the equatorial westerly anomalies) by reallocating anomalous atmospheric heating and SST gradient along the equator. This structural change amplifies the ENSO cycle and prolongs the oscillation period by enhancing the coupled instability and delaying transitions from a warm to a cold state or vice versa. The changes in the mean currents and upwelling reduce the effect of the zonal temperature advection while enhance that of the vertical advection; thus, the prevailing westward propagation is replaced by eastward propagation or standing oscillation. Our results suggest a critical role of the atmospheric bridge that rapidly conveys the influences of extratropical decadal variations to the tropics, and the possibility that the Pacific climate shift might have affected El Nino properties in the late 1970s by changing the background tropical winds and the associated equatorial upwelling.
Wang C. Z., L. P. Zhang, S. K. Lee, L. X. Wu, and C. R. Mechoso, 2014: A global perspective on CMIP5 climate model biases. Nature Clim.Change, 4, 201- 205.
Zhang W. J., F. F. Jin, 2012: Improvements in the CMIP5 simulations of ENSO-SSTA meridional width. Geophys. Res. Lett., 39,L23704, doi: 10.1029/2012GL053588.10.1029/2012GL0535884bcc43f5b9a26e659c92b8ab48855777http%3A%2F%2Fonlinelibrary.wiley.com%2Fdoi%2F10.1029%2F2012GL053588%2Ffullhttp://onlinelibrary.wiley.com/doi/10.1029/2012GL053588/fullABSTRACT The recent study demonstrated the existence of a systematical narrow bias in the simulated El Niño-Southern Oscillation (ENSO) meridional width of surface temperature anomaly (SSTA) of ENSO by the models participating in Phase 3 of the Coupled Model Inter-comparison Project (CMIP3). The current models developed for Phase 5 of the CMIP (CMIP5) still have this narrow bias in ENSO width relative to the observation, but with a modest improvement over previous models. The improvement can partly be attributed to a better simulation in trade wind, and partly to a better simulation in ENSO period. It has also been demonstrated that the models with a better performance in ENSO width tend to simulate the precipitation response to ENSO over the off-equatorial eastern Pacific more realistically.
Zhang T., D. Z. Sun, 2014: ENSO asymmetry in CMIP5 models. J.Climate, 27, 4070- 4093.10.1175/JCLI-D-13-00454.15d86fc161edf196b84bc5acd5d12af28http%3A%2F%2Fadsabs.harvard.edu%2Fabs%2F2014JCli...27.4070Zhttp://adsabs.harvard.edu/abs/2014JCli...27.4070ZThe El Ni01±o-La Ni01±a asymmetry is evaluated in 14 coupled models from phase 5 of the Coupled Model Intercomparison Project (CMIP5). The results show that an underestimate of ENSO asymmetry, a common problem noted in CMIP3 models, remains a common problem in CMIP5 coupled models. The weaker ENSO asymmetry in the models primarily results from a weaker SST warm anomaly over the eastern Pacific and a westward shift of the center of the anomaly. In contrast, SST anomalies for the La Ni01±a phase are close to observations. Corresponding Atmospheric Model Intercomparison Project (AMIP) runs are analyzed to understand the causes of the underestimate of ENSO asymmetry in coupled models. The analysis reveals that during the warm phase, precipitation anomalies are weaker over the eastern Pacific, and westerly wind anomalies are confined more to the west in most models. The time-mean zonal winds are stronger over the equatorial central and eastern Pacific for most models. Wind-forced ocean GCM experiments suggest that the stronger time-mean zonal winds and weaker asymmetry in the interannual anomalies of the zonal winds in AMIP models can both be a contributing factor to a weaker ENSO asymmetry in the corresponding coupled models, but the former appears to be a more fundamental factor, possibly through its impact on the mean state. The study suggests that the underestimate of ENSO asymmetry in the CMIP5 coupled models is at least in part of atmospheric origin.
Zhang T., D. Z. Sun, R. Neale, and P. Rasch, 2009: An evaluation of ENSO asymmetry in the Community Climate System Models: A view from the subsurface. J. Climate,22, 5933-5961, doi: 10.1175/2009JCLI2933.1.10.1175/2009JCLI2933.1afe6b01f8e8f612d3d71c853feb3ff4fhttp%3A%2F%2Fwww.cabdirect.org%2Fabstracts%2F20103007987.htmlhttp://www.cabdirect.org/abstracts/20103007987.htmlAbstract The asymmetry between El Niño and La Niña is a key aspect of ENSO that needs to be simulated well by models in order to fully capture the role of ENSO in the climate system. Here the asymmetry between the two phases of ENSO in five successive versions of the Community Climate System Model (CCSM1, CCSM2, CCSM3 at T42 resolution, CCSM3 at T85 resolution, and the latest CCSM3 + NR, with the Neale and Richter convection scheme) is evaluated. Different from the previous studies, not only is the surface signature of ENSO asymmetry examined, but so too is its subsurface signature. By comparing the differences among these models as well as the differences between the models and the observations, an understanding of the causes of the ENSO asymmetry is sought. An underestimate of the ENSO asymmetry is noted in all of the models, but the latest version with the Neale and Richter scheme (CCSM3 + NR) is getting closer to the observations than the earlier versions. The net surface heat flux is found to damp the asymmetry in the SST field in both the models and observations, but the damping effect in the models is weaker than that in the observations, thus excluding a role of the surface heat flux in contributing to the weaker asymmetry in the SST anomalies associated with ENSO. Examining the subsurface signatures of ENSO-he thermocline depth and the associated subsurface temperature for the western and eastern Pacific-eveals the same bias; that is, the asymmetry in the models is weaker than that in the observations. The analysis of the corresponding Atmospheric Model Intercomparison Project (AMIP) runs in conjunction with the coupled runs suggests that the weaker asymmetry in the subsurface signatures in the models is related to the lack of asymmetry in the zonal wind stress over the central Pacific, which in turn is due to a lack of sufficient asymmetry in deep convection (i.e., the nonlinear dependence of the deep convection on SST). In particular, the lack of a westward shift in the deep convection in the models in response to a cold phase SST anomaly is found as a common factor that is responsible for the weak asymmetry in the models. It is also suggested that a more eastward extension of the deep convection in response to a warm phase SST anomaly may also help to increase the asymmetry of ENSO. The better performance of CCSM3 + NR is apparently linked to an enhanced convection over the eastern Pacific during the warm phase of ENSO. Apparently, either a westward shift of deep convection in response to a cold phase SST anomaly or an increase of convection over the eastern Pacific in response to a warm phase SST anomaly leads to an increase in the asymmetry of zonal wind stress and therefore an increase in the asymmetry of subsurface signal, favoring an increase in ENSO asymmetry.