Seasonal and Intraseasonal Variations of East Asian Summer Monsoon Precipitation Simulated by a Regional Air-Sea Coupled Model

The performance of a regional air-sea coupled model, comprising the Regional Integrated Environment Model System （RIEMS） and the Princeton Ocean Model （POM）, in simulating the seasonal and intraseasonal variations of East Asian summer monsoon （EASM） rainfall was investigated. Through comparisons of the model results among the coupled model, the uncoupled RIEMS, and observations, the impact of air-sea coupling on simulating the EASM was also evaluated. Results showed that the regional air sea coupled climate model performed better in simulating the spatial pattern of the precipitation climatology and produced more realistic variations of the EASM rainfall in terms of its amplitude and principal EOF modes. The coupled model also showed greater skill than the uncoupled RIEMS in reproducing the principal features of climatological intraseasonal oscillation （CISO） of EASM rainfall, including its dominant period, intensity, and northward propagation. Further analysis indicated that the improvements in the simulation of the EASM rainfall climatology and its seasonal variation in the coupled model were due to better simulation of the western North Pacific Subtropical High, while the improvements of CISO simulation were owing to the realistic phase relationship between the intraseasonal convection and the underlying SST resulting from the air-sea coupling.

The climatology and interannual variability of the East Asian summer monsoonsimulated by a weakly coupled data assimilation system

With the motivation to improve the simulation of the East Asian summer monsoon(EASM) in coupled climate models, oceanic data assimilation(DA) was used in CAS-ESM-C(Chinese Academy of Sciences–Earth System Model–Climate Component) in this study. Observed sea surface temperature was assimilated into CAS-ESM-C. The climatology and interannual variability of the EASM simulated in CAS-ESM-C with DA were compared with a traditional AMIP-type run.Results showed that the climatological spatial pattern and annual cycle of precipitation in the western North Paci?c, and the ENSO-related and EASM-related EASM circulation and precipitation, were largely improved. As shown in this study, air–sea coupling is important for EASM simulation. In addition, oceanic DA synchronizes the coupled model with the real world without breaking the air–sea coupling process. These two successful factors make the assimilation experiment a more reasonable experimental design than traditional AMIP-type simulations.

Evaluation of the interannual variability in the East Asian summer monsoon in AMIP and historical experiments of CAS FGOALS-f3-L

对东亚夏季季风(EASM)模拟的评估可以提高我们对亚洲季风动力和气候模拟的理解.在这项研究中,通过使用中国科学院(CAS)全球海洋-大气-陆地系统(FGOALS-f3-L)模式参加的第六次耦合模式相互比较计划(CMIP6)中的大气模式相互比较计划(AMIP)和历史(historical)试验,明确了EASM的年际变率的模拟能力.通过多变量经验正交函数(MV-EOF)分析发现,观测的EASM的主导模态为西太平洋上的太平洋-日本模态,并伴有局部反气旋异常.主导模态的方差贡献率为24.6%.历史(historical)试验可以基本再现这种空间模态,其方差贡献率较AMIP试验更接近于观测.与AMIP试验相比,历史(historical)试验还能更好地模拟EASM变率的时间频率.然而,由于历史(historical)模拟没有在积分开始时应用初始化过程,而AMIP试验受到海表面温度(SST)的约束,因此主成分(PC1)的位相在历史(historical)试验中没有得到较好地再现.进一步分析发现,印度洋和西太平洋热带地区的海气相互作用对EASM的模拟非常重要,而EASM气候变率的模拟可能与厄尔尼诺-南方涛动(ENSO)的模拟能力有关,这值得进一步分析.

Diversity of the Coupling Wheels in the East Asian Summer Monsoon on the Interannual Time Scale: Challenge of Summer Rainfall Forecasting in China

Two types of three-dimensional circulation of the East Asian summer monsoon(EASM) act as the coupling wheels determining the seasonal rainfall anomalies in China during 1979–2015. The first coupling mode features the interaction between the Mongolian cyclone over North Asia and the South Asian high(SAH) anomalies over the Tibetan Plateau at 200 hPa. The second mode presents the coupling between the anomalous low-level western Pacific anticyclone and upperlevel SAH via the meridional flow over Southeast Asia. These two modes are responsible for the summer rainfall anomalies over China in 24 and 7 out of 37 years, respectively. However, the dominant SST anomalies in the tropical Pacific, the Indian Ocean, and the North Atlantic Ocean fail to account for the first coupling wheel's interannual variability, illustrating the challenges in forecasting summer rainfall over China.

CMIP5/AMIP GCM Simulations of East Asian Summer Monsoon

The East Asian summer monsoon （EASM） is a distinctive component of the Asian climate system and critically influences the economy and society of the region.To understand the ability of AGCMs in capturing the major features of EASM,10 models that participated in Coupled Model Intercomparison Project/Atmospheric Model Intercomparison Project （CMIP5/AMIP）,which used observational SST and sea ice to drive AGCMs during the period 1979-2008,were evaluated by comparing with observations and AMIP Ⅱ simulations.The results indicated that the multi-model ensemble （MME） of CMIP5/AMIP captures the main characteristics of precipitation and monsoon circulation,and shows the best skill in EASM simulation,better than the AMIP Ⅱ MME.As for the Meiyu/Changma/Baiyu rainbelt,the intensity of rainfall is underestimated in all the models.The biases are caused by a weak western Pacific subtropical high （WPSH） and accompanying eastward southwesterly winds in group Ⅰ models,and by a too strong and west-extended WPSH as well as westerly winds in group Ⅱ models.Considerable systematic errors exist in the simulated seasonal migration of rainfall,and the notable northward jumps and rainfall persistence remain a challenge for all the models.However,the CMIP5/AMIP MME is skillful in simulating the western North Pacific monsoon index （WNPMI）.

THE ANALYSIS OF MECHANISM OF IMPACT OF AEROSOLS ON EAST ASIAN SUMMER MONSOON INDEX AND ONSET

RegCM4.3, a high-resolution regional climate model, which includes five kinds of aerosols(dust, sea salt,sulfate, black carbon and organic carbon), is employed to simulate the East Asian summer monsoon(EASM) from 1995 to 2010 and the simulation data are used to study the possible impact of natural and anthropogenic aerosols on EASM.The results show that the regional climate model can well simulate the EASM and the spatial and temporal distribution of aerosols. The EASM index is reduced by about 5% by the natural and anthropogenic aerosols and the monsoon onset time is also delayed by about a pentad except for Southeast China. The aerosols heat the middle atmosphere through absorbing solar radiation and the air column expands in Southeast China and its offshore areas. As a result, the geopotential height decreases and a cyclonic circulation anomaly is generated in the lower atmosphere. Northerly wind located in the west of cyclonic circulation weakens the low-level southerly wind in the EASM region. Negative surface radiative forcing due to aerosols causes downward motion and an indirect meridional circulation is formed with the low-level northerly wind and high-level southerly wind anomaly in the north of 25° N in the monsoon area, which weakens the vertical circulation of EASM. The summer precipitation of the monsoon region is significantly reduced,especially in North and Southwest China where the value of moisture flux divergence increases.

Impact of Different East Asian Summer Monsoon Circulations on Aerosol-Induced Climatic Effects

The different spatial distributions of aerosol-induced direct radiative forcing and climatic effects in a weak （2003） and a strong （2006） East Asian summer monsoon （EASM） circulation were simulated using a high-resolution regional climate model （RegCM3）.Results showed that the atmospheric circulations of summer monsoon have direct relations with transport of aerosols and their climatic effects.Both the top-of-the-atmosphere （TOA） and the surface-negative radiative forcing of aerosols were stronger in weak EASM circulations.The main difference in aerosol-induced negative forcing in two summers varied between 2 and 14 W m-2 from the Sichuan Basin to North China,where a maximum in aerosol-induced negative forcing was also noticed in the EASM-dominated areas.The spatial difference in the simulated aerosol optical depth （AOD） in two summers generally showed the similar pictures.Surface cooling effects induced by aerosols were spatially more uniform in weak EASM circulations and cooler by about 1-4.5℃.A preliminary analysis here indicated that a weaker low-level wind speed not conducive to the transport and diffusion of aerosols could make more contributions to the differences in the two circulations.

The Interannual Variability of East Asian Monsoon and Its Relationship with SST in a Coupled Atmosphere-Ocean-Land Climate Model

Based on a 200 year simulation and reanalysis data (1980–1996), the general characteristics of East Asian monsoon (EAM) were analyzed in the first part of the paper. It is clear from this re-search that the South Asian monsoon (SAM) defined by Webster and Yang (1992) is geographically and dynamically different from the East Asian monsoon (EAM). The region of the monsoon defined by Webster and Yang (1992) is located in the tropical region of Asia (40–110°E, 10–20°N), including the Indian monsoon and the Southeast Asian monsoon, while the EAM de-fined in this paper is located in the subtropical region of East Asia (110–125°E, 20–40°N). The components and the seasonal variations of the SAM and EAM are different and they characterize the tropical and subtropical Asian monsoon systems respectively. A suitable index (EAMI) for East Asian monsoon was then defined to describe the strength of EAM in this paper. In the second part of the paper, the interannual variability of EAM and its relationship with sea surface temperature (SST) in the 200 year simulation were studied by using the composite method, wavelet transformation, and the moving correlation coefficient method. The summer EAMI is negatively correlated with ENSO (El Nino and Southern Oscillation) cycle represented by the NINO3 sea surface temperature anomaly (SSTA) in the preceding April and January, while the winter EAM is closely correlated with the succeeding spring SST over the Pacific in the coupled model. The general differences of EAM between El Nino and La Nina cases were studied in the model through composite analysis. It was also revealed that the dominating time scales of EAM variability may change in the long-term variation and the strength may also change. The anoma-lous winter EAM may have some correlation with the succeeding summer EAM, but this relation-ship may disappear sometimes in the long-term climate variation. Such time-dependence was found in the relationship between EAM and SST in the long-term climate simulation as well. Key words East Asian monsoon - Interannual variability - Coupled climate model The author wishes to thank Profs. Wu G.X., Zhang X.H., and Dr. Yu Y.Q. for providing the coupled model re-sults. Dr. Yu also kindly provided assistance in using the model output. This work was supported jointly by the Na-tional Natural Science Foundation of China key project ’ The analysis on the seasonal-to-interannual variation of the general circulation’ under contract 49735160 and Chinese Academy of Sciences key project ’ The Interannual Va-riability and Predictability of East Asian Monsoon’.

An Assessment on the Performance of IPCC AR4 Climate Models in Simulating Interdecadal Variations of the East Asian Summer Monsoon

Observations from several data centers together with a categorization method are used to evaluate the IPCC AR4 （Intergovernmental Panel on Climate Change, the Fourth Assessment Report） climate models＇ performance in simulating the interdecadal variations of summer precipitation and monsoon circulation in East Asia. Out of 19 models under examination, 9 models can relatively well reproduce the 1979-1999 mean June-July-August （JJA） precipitation in East Asia, but only 3 models （Category-1 models） can capture the interdecadal variation of precipitation in East Asia. These 3 models are： GFDL-CM2.0, MIROC3.2 （hires）, and MIROC3.2 （medres）, among which the GFDL-CM2.0 gives the best performance. The reason for the poor performance of most models in simulating the East Asian summer monsoon interdecadal variation lies in that the key dynamic and thermal-dynamic mechanisms behind the East Asian monsoon change are missed by the models, e.g., the large-scale tropospheric cooling and drying over East Asia. In contrast, the Category-1 models relatively well reproduce the variations in vertical velocity and water vapor over East Asia and thus show a better agreement with observations in simulating the pattern of ＂wet south and dry north＂ in China in the past 20 years. It is assessed that a single model＇s performance in simulating a particular variable has great impacts on the ensemble results. More realistic outputs can be obtained when the multi-model ensemble is carried out using a suite of well-performing models for a specific variable, rather than using all available models. This indicates that although a multi-model ensemble is in general better than a single model, the best ensemble mean cannot be achieved without looking into each member model＇s performance.

Impacts of boundary layer parameterization schemes and air-sea coupling on WRF simulation of the East Asian summer monsoon

The planetary boundary layer （PBL） scheme in the regional climate model （RCM） has a significant impact on the interactions and exchanges of moisture, momentum, and energy between land, ocean, and atmosphere; however, its uncertainty will cause large systematic biases of RCM. Based on the four different PBL schemes （YSU, ACM2, Boulac, and MYJ） in Weather Research and Forecasting （WRF） model, the impacts of these schemes on the simulation of circulation and precipitation during the East Asian summer monsoon （EASM） are investigated. The simulated results of the two local turbulent kinetic energy （TKE） schemes, Boulac and MYJ, are more consistent with the observations than those in the two nonlocal closure schemes, YSU and ACM2. The former simulate more reasonable low-level southwesterly flow over East China and west pacific subtropical high （WPSH） than the latter. As to the modeling of summer monsoon precipitation, both the spatial distributions and temporal evolutions from Boulac and MTT are also better than those in YSU and ACM2 schemes. In addition, through the comparison between YSU and Boulac experiments, the differences from the results of EASM simulation are more obvious over the oceanic area. In the experiments with the nonlocal schemes YSU and ACM2, the boundary layer mixing processes are much stronger, which lead to produce more sea surface latent heat flux and enhanced convection, and finally induce the overestimated precipitation and corresponding deviation of monsoon circulation. With the further study, it is found that the absence of air-sea interaction in WRF may amplify the biases caused by PBL scheme over the ocean. Consequently, there is a reduced latent heat flux over the sea surface and even more reasonable EASM simulation, if an ocean model coupled into WRF.

An Introduction to the Coupled Model FGOALS1.1-s and Its Performance in East Asia

The spectral version 1.1 of the Flexible Global Ocean–atmosphere–land System （FGOALS1.1-s） model was developed in the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophys- ical Fluid Dynamics at the Institute of Atmospheric Physics （LASG/IAP）. This paper reports the major modifications to the physical parameterization package in its atmospheric component, including the radiation scheme, convection scheme, and cloud scheme. Furthermore, the simulation of the East Asian Summer Monsoon （EASM） by FGOALS1.1-s is examined, both in terms of climatological mean state and interannual variability. The results indicate that FGOALS1.1-s exhibits significant improvements in the simulation of the balance of energy at the top of the atmosphere： the net radiative energy flux at the top was 0.003 W m-2 in the 40 years fully coupled integration. The distribution of simulated sea surface temperature was also quite reasonable, without obvious climate drift. FGOALS1.1-s is also capable of capturing the major features of the climatological mean state of the EASM： major rainfall maximum centers, the annual cycle of precipitation, and the lower-level monsoon circulation flow were highly consistent with observations in the EASM region. Regarding interannual variability, simulation of the EASM leading patterns and their relationship with sea surface temperature was examined. The results show that FGOALS1.1-s can reproduce the first leading pattern of the EASM and its close relationship with the decaying phase of the ENSO. However, the model lacked the ability to capture either the second major mode of the EASM or its relationship with the developing phase of the ENSO.

Simulation of East Asian Summer Monsoon with IAP CGCM

East Asian summer monsoon simulated by a coupled ocean-atmosphere general circulation model developed in the Institute of Atmospheric Physics (IAP CGCM) is analyzed. The precipitation, low-level streamline field, sea level pressure, low-level temperature and mixing ratio are compared with the observed ones respectively. The results show that IAP CGCM can simulate most features of summer monsoon circulation, but it still has some important systematic errors. The simulated Somali jet tends to be much weak and lies too far south. The cross-equatorial flows between 120 o E and dateline are also too weaker in the model than those in reality, while the South Asia monsoon low is stronger than that in the observation and reaches further east. At the same time, the subtropical high in the western Pacific extends too far west and north. Accompanied by these deviations in tropical and subtropical zones, the westerly troughs in the middle and high latitudes affect further southerly regions in China than those observed. All these deficiencies in simulating summer monsoon circulation result in the errors in modelled precipitation in East Asia, which include the underestimation of precipitation over East Asia in summer, the premature emergence of maximum precipitation and the further southerly rainfall belt in East Asia than the observed one. So the most obvious drawbeck of the model is the apparent underestimation of Meiyu frontal rainfall.

Response of the East Asian summer monsoon to large volcanic eruptions during the last millennium

The responses of the East Asian summer monsoon(EASM)to large volcanic eruptions were analyzed using a millennial simulation with the FGOALS-gl climate system model.The model was driven by both natural(solar irradiance,volcanic eruptions)and anthropogenic(greenhouse gases,sulfate aerosols)forcing agents.The results showed cooling anomalies after large volcanic eruptions almost on a global scale.The cooling over the continental region is stronger than that over the ocean.The precipitation generally decreases in the tropical and subtropical regions in the first summer after large volcanic eruptions.Cooling with amplitudes up to-0.3°C is seen over eastern China in the first summer after large volcanic eruptions.The East Asian continent is dominated by northeasterly wind anomalies and the corresponding summer rainfall exhibits a coherent reduction over the whole of eastern China.An analysis of the surface heat flux suggested the reduction in summer precipitation over eastern China can be attributed to a decrease of moisture vapor over the tropical oceans,and the weakening of the EASM may be attributed to the reduced land–sea thermal contrast after large volcanic eruptions.

A Possible Impact of Cooling over the Tibetan Plateau on the Mid-Holocene East Asian Monsoon Climate

By using a 9-level global atmospheric general circulation model developed at the Institute of Atmospheric Physics （IAP9L-AGCM） under the Chinese Academy of Sciences, the authors investigated the response of the East Asian monsoon climate to changes both in orbital forcing and the snow and glaciers over the Tibetan Plateau at the mid-Holocene, about 6000 calendar years before the present （6 kyr BP）. With the Earth＇s orbital parameters appropriate for the mid-Holocene, the IAP9L-AGCM computed warmer and wetter conditions in boreal summer than for the present day. Under the precondition of continental snow and glacier cover existing over part of the Tibetan Plateau at the mid-Holocene, the authors examined the regional climate response to the Tibetan Plateau cooling. The simulations indicated that climate changes in South Asia and parts of central Asia as well as in East Asia are sensitive to the Tibetan Plateau cooling at the mid-Holocene, showing a significant decrease in precipitation in northern India, northern China and southern Mongolia and an increase in Southeast Asia during boreal summer. The latter seems to correspond to the weakening, southeastward shift of the Asian summer monsoon system resulting from reduced heat contrast between the Eurasian continent and the Pacific and Indian Oceans when a cooling over the Tibetan Plateau was imposed. The simulation results suggest that the snow and glacier environment over the Tibetan Plateau is an important factor for mid-Holocene climate change in the areas highly influenced by the Asian monsoon.

Different Asian Monsoon Rainfall Responses to Idealized Orography Sensitivity Experiments in the HadGEM3-GA6 and FGOALS-FAMIL Global Climate Models

Recent work has shown the dominance of the Himalaya in supporting the Indian summer monsoon （ISM）, perhaps by surface sensible heating along its southern slope and by mechanical blocking acting to separate moist tropical flow from drier midlatitnde air. Previous studies have also shown that Indian snmmer rainfall is largely unaffected in sensitivity experiments that remove only the Tibetan Plateau. However, given the large biases in simulating the monsoon in CMIP5 models, such results may be model dependent. This study investigates the impact of orographic forcing from the Tibetan Plateau, Himalaya and Iranian Plateau on the ISM and East Asian snmmer monsoon （EASM） in the UK Met Office＇s HadGEM3-GA6 and China＇s Institute of Atmospheric Physics FGOALS-FAMIL global climate models. The models chosen featnre oppositesigned biases in their simulation of the ISM rainfall and circulation climatology. The changes to ISM and EASM circulation across the sensitivity experiments are similar in both models and consistent with previous studies. However, considerable differences exist in the rainfall responses over India and China, and in the detailed aspects such as onset and retreat dates. In particular, the models show opposing changes in Indian monsoon rainfall when the Himalaya and Tibetan Plateau orography are removed. Our results show that a multi-model approach, as suggested in the forthcoming Global Monsoon Model Intercomparison Project （GMMIP） associated with CMIP6, is needed to clarify the impact of orographic forcing on the Asian monsoon and to fully understand the implications of model systematic error.

A Possible Role of Solar Radiation and Ocean in the Mid-Holocene East Asian Monsoon Climate

An atmospheric general circulation model (AGCM) and an oceanic general circulation model (OGCM) are asynchronously coupled to simulate the climate of the mid-Holocene period. The role of the solar radiation and ocean in the mid-Holocene East Asian monsoon climate is analyzed and some mechanisms are revealed. At the forcing of changed solar radiation induced by the changed orbital parameters and the changed SST simulated by the OGCM, compared with when there is orbital forcing alone, there is more precipitation and the monsoon is stronger in the summer of East Asia, and the winter temperature increases over China. These agree better with the reconstructed data. It is revealed that the change of solar radiation can displace northward the ITCZ and the East Asia subtropical jet, which bring more precipitation over the south of Tibet and North and Northeast China. By analyzing the summer meridional latent heat transport, it is found that the influence of solar radiation change is mainly to increase the convergence of atmosphere toward the land, and the influence of SST change is mainly to transport more moisture to the sea surface atmosphere. Their synergistic effect on East Asian precipitation is much stronger than the sum of their respective effects.

THE EFFECTS OF TIBETAN PLATEAU ON THE ANOMALOUS VARIATION OF ASIAN MONSOON IN A COUPLED OCEAN-ATMOSPHERE SYSTEM

Experimental predictions with a hybrid coupled ocean-atmosphere model(L9R15 AGCM-ZC ocean model)were performed for the 1986/87 El Nino event and the 1988/89 La Nina event with and without the Tibetan Plateau respectively(called TP FORC and NTP FORC hereinafter). Comparison shows that,to some extent,the existence of the Tibetan Plateau orography weakens or restrains(strengthens or facilitates)the formation of the anomalous circulation of Asian monsoon during El Nino(La Nina)period.Opposite results are found in the uncoupled AGCM simulation.

A Robustness Analysis of CMIP5 Models over the East Asia-Western North Pacific Domain

The Coupled Model Intercomparison Project （CMIP） is an international community-based infrastructure that supports climate model intercomparison, climate variability, climate prediction, and climate projection. Improving the performance of climate models over East Asia and the western North Pacific has been a challenge for the climate-modeling community. In this paper, we provide a synthesis robustness analysis of the climate models participating in CMIP-Phase 5 （CMIP5）. The strengths and weaknesses of the CMIP5 models are assessed from the perspective of climate mean state, interannual variability, past climate change during the mid-Pliocene （MP） and the last millennium, and climate projection. The added values of regional climate models relative to the driving global climate models are also assessed. Although an encouraging increase in credibility and an improvement in the simulation of mean states, interannual variability, and past climate changes are visible in the progression from CMIP3 to CMIPS, some previously noticed biases such as the ridge position of the western North Pacific subtropical high and the associated rainfall bias are still evident in CMIP5 models. Weaknesses are also evident in simulations of the interannual amplitude, such as El Nino- Southern Oscillation （ENSO）-monsoon relationships. Coupled models generally show better results than standalone atmospheric models in simulating both mean states and interannual variability. Multi-model intercomparison indicates significant uncertainties in the future projection of climate change, although precipitation increases consistently across models constrained by the Clausius-Clapeyron relation. Regional ocean-atmosphere coupled models are recommended for the dynamical downscaling of climate change oroiections over the East Asia-western North Pacific domain.

Simulation of Precipitation in Monsoon Regions of China by CMIP3 Models

The output of 25 models used in the Coupled Model Intercomparison Project phase 3 (CMIP3) were evaluated,with a focus on summer precipitation in eastern China for the last 40 years of the 20th century.Most mod-els failed to reproduce rainfall associated with the East Asian summer monsoon (EASM),and hence the seasonal cycle in eastern China,but provided reasonable results in Southwest (SW) and Northeast China (NE).The simula-tions produced reasonable results for the Yangtze-Huai (YH) Basin area,although the Meiyu phenomenon was underestimated in general.One typical regional phe-nomenon,a seasonal northward shift in the rain belt from early to late summer,was completely missed by most models.The long-term climate trends in rainfall over eastern China were largely underestimated,and the ob-served geographical pattern of rainfall changes was not reproduced by most models.Precipitation extremes were evaluated via parameters of fitted GEV (Generalized Ex-treme Values) distributions.The annual extremes were grossly underestimated in the monsoon-dominated YH and SW regions,but reasonable values were calculated for the North China (NC) and NE regions.These results suggest a general failure to capture the dynamics of the EASM in current coupled climate models.Nonetheless,models with higher resolution tend to reproduce larger decadal trends and annual extremes of precipitation in the regions studied.

海气相互作用在模式FGOALS-g3模拟东亚夏季风及其对前冬El Niño响应中的贡献

本文基于观测、再分析资料和中国科学院大气物理研究所大气科学和地球流体力学数值模拟国家重点实验室(LASG)最新版本气候系统模式FGOALS-g3,探究了海气相互作用在模拟东亚夏季风及其对前冬El Niño响应中的贡献。大气环流模式(AGCM)模拟的气候态夏季风雨带偏东,东亚季风区表现为干偏差,耦合模式(CGCM)虽模拟出了夏季风雨带的位置,但降水仍偏弱。AGCM由于缺乏海气耦合过程,夏季西北太平洋地区对流模拟过强,使得副热带高压(简称副高)偏东、南中国海季风槽偏东,造成东亚夏季风雨带偏东;东亚陆地区域水汽偏少,也是降水干偏差的一个重要原因,此两项可以解释70%以上的干偏差。在考虑海气相互作用后,西北太平洋的降水正异常减弱了局地海表温度,因此CGCM显著改进了副高以及南中国海季风槽偏东等偏差,使得夏季风雨带位置得到改进,季风区降水干偏差减小了36%,但由于水汽偏少,水汽纬向输送偏少,东亚季风区仍维持着显著的干偏差。另一方面,对前冬El Niño的响应,CGCM能够再现El Niño衰减年夏季印度—西太平洋电容器效应(IPOC机制)对西北太平洋异常反气旋(WNPAC)的维持作用及偶极型分布的降水异常。而AGCM中夏季西北太平洋以及孟加拉湾、印度半岛周围海域对流对于海温的响应过于敏感,一方面西北太平洋局地暖异常造成的对流质量输送一定程度上抑制了WNPAC的建立,另一方面孟加拉湾、印度半岛周围海域过强的上升异常,通过局地环流,抑制了其南侧印度洋的对流异常,导致无法模拟出IPOC机制对衰减年夏季WNPAC的维持作用。因此,缺乏海气耦合过程是AGCM不能模拟出东亚夏季风对前冬El Niño滞后响应的关键原因。