Simulation of Asian Monsoon Seasonal Variations with Climate Model R42L9/LASG

The seasonal variations of the Asian monsoon were explored by applying the atmospheric general circulation model R42L9 that was developed recently at the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics, Institute of Atmospheric Physics, Chinese Academy of Sciences (LASG/IAP/CAS). The 20-yr (1979–1998) simulation was done using the prescribed 20-yr monthly SST and sea-ice data as required by Atmospheric Model Intercomparison Project (AMIP) II in the model. The monthly precipitation and monsoon circulations were analyzed and compared with the observations to validate the model’s performance in simulating the climatological mean and seasonal variations of the Asian monsoon. The results show that the model can capture the main features of the spatial distribution and the temporal evolution of precipitation in the Indian and East Asian monsoon areas. The model also reproduced the basic patterns of monsoon circulation. However, some biases exist in this model. The simulation of the heating over the Tibetan Plateau in summer was too strong. The overestimated heating caused a stronger East Asian monsoon and a weaker Indian monsoon than the observations. In the circulation ?elds, the South Asia high was stronger and located over the Tibetan Plateau. The western Paci?c subtropical high was extended westward, which is in accordance with the observational results when the heating over the Tibetan Plateau is stronger. Consequently, the simulated rainfall around this area and in northwest China was heavier than in observations, but in the Indian monsoon area and west Paci?c the rainfall was somewhat de?cient.

T_(BB) DATA-REVEALED FEATURES OF ASIAN-AUSTRALIAN MONSOON SEASONAL TRANSITION AND ASIAN SUMMER MONSOOM ESTABLISHMENT

Based on TBB data from Meteorological Institute Research of Japan, study is carried out of the features of seasonal transition of Asian-Australian monsoons and Asian summer monsoon establishment,indicating that the transition begins as early as in April, followed by abrupt change in May-June; the Asian summer monsoon situation is fully established in June. The winter convective center in Sumatra moved steadily northwestward across the "land bridge" of the maritime continent and the Indo-China Peninsula as time goes from winter to summer, thus giving rise to the change in large scale circulations that is responsible for the summer monsoon establishment over SE Asia and India; the South China Sea to the western Pacific summer monsoon onset bears a close relation to the active convection in the Indo China Peninsula and steady eastward retreat of the subtropical TBB high-value band,corresponding to the western Pacific subtropical high.

Role of mesoscale eddies on atmospheric convection during summer monsoon season over the Bay of Bengal: A case study

Our study aims to understand the variability of oceanic mesoscale eddies during contrasting(2009 and 2013)monsoon seasons and the role of such eddies on atmospheric deep convection over the Bay of Bengal(BoB).Oceanic eddies are detected and tracked using sea surface height anomalies(SSHA),by employing the Okubo-Weiss parameter eddy detection method.Significant differences in the SSHA and eddy activity are evident during the contrasting monsoon years.During the year 2013(2009),anticyclonic eddies are predominant(absent)in the eastern BoB and longer(shorter)lifespans of cyclonic eddies are observed in the northern and western BoB.Analysis of time-longitude SSHA and zonal wind stress reveals the presence of strong(weak)equatorial downwelling Kelvin waves,coastal Kelvin waves and Rossby waves in the BoB during 2013(2009)Indian summer monsoon(ISM).The variability of eddies in the BoB during contrasting monsoons is attributed by the remote forcing effect of planetary scale waves.Our study is extended to investigate the associated atmospheric deep convection over the regions of cyclonic and anticyclonic eddies.Lag-correlations demonstrates that SSHA leads the outgoing longwave radiation by four days over anticyclonic eddy regions.Findings from the present study provide new insight into the internal dynamics of the ocean.

SEASONAL TRANSITION OF EAST ASIAN SUBTROPICAL MONSOON AND ITS POSSIBLE MECHANISM

The NCEP/NCAR reanalysis datasets and Climate Prediction Center(CPC) Merged Analysis of Precipitation(CMAP) rain data are used to investigate the large scale seasonal transition of East Asian subtropical monsoon(EASM) and its possible mechanism.The key region of EASM is defined according to the seasonal transition feature of meridional wind.By combining the 'thermal wind' formula and the 'thermal adaptation' equation,a new 'thermal-wind-precipitation' relation is deduced.The area mean wind directions and thermal advections in different seasons are analyzed and it is shown that in summer(winter) monsoon period,the averaged wind direction in the EASM region varies clockwise(anticlockwise) with altitude,and the EASM region is dominated by warm(cold) advection.The seasonal transition of the wind direction at different levels and the corresponding meridional circulation consistently indicates that the subtropical summer monsoon is established between the end of March and the beginning of April.Finally,a conceptual schematic explanation for the mechanism of seasonal transition of EASM is proposed.

Seasonal Transition of Summer Rainy Season over Indochina and Adjacent Monsoon Region

The mean onset and withdrawal of summer rainy season over the Indochina Peninsula were investigated using 5-day averaged rainfall data (1975-87). The mean seasonal transition process during onset and retreat phases in Indochina, India and the South China Sea is also examined using 5-day mean OLR (1975-87) and 850 hPa wind (1980-88) data. It was found that the onset of summer rainy season begins earlier in the inland region of Indochina (Thailand) in late April to early May than in the coastal region along the Bay of Bengal. This early onset of rainy season is due to pre-monsoon rain under the mid-latitude westerly wind regime. The full summer monsoon circulation begins to establish in mid-May, causing active convective activity both over the west coast of Indochina and the central South China Sea. In case of withdrawal, the earliest retreat of summer rainy season is found in the central northern part of Indochina in late September. The wind field, on the other hand, already changes to easterlies in the northern South China Sea in early September. This easterly wind system covers the eastern part of Indochina where post-monsoon rain is still active. In late October, the wind field turns to winter time situation, but post monsoon rain still continues in the southern part of the Indochina Peninsula until late November.

Seasonal and Interannual Variations of Upper Tropospheric Water Vapor Band Brightness Temperature over the Global Monsoon Regions

The upper-troposphere water vapor (UTWV) band brightness temperature (BT) dataset derived from the High-resolution Infrared Radiation Sounder (HIRS) channel 12 of the National Oceanic and Atmospheric Administration (NOAA) polar satellites from 1979 to 1995 is used to analyze the seasonal and interannual variations for the global monsoon regions. Results show that (i) there are three major regions where the UTWV band BT varies significantly with season, i.e., South Asia, the western coastal South-North America tropical region and the low-latitude African region; (ii) UTWV band BT clearly reveals the water vapor temporal/spatial features as well as the atmospheric circulation structure over the low-latitude during the monsoon onset; and (iii) there is a remarkable relationship between the interannual variation of the UTWV band BT over the monsoon regions and the sea surface temperature anomaly in the eastern equatorial Pacific.

Effect of climate change on seasonal monsoon in Asia and its impact on the variability of monsoon rainfall in Southeast Asia

Global warming and climate change is one of the most extensively researched and discussed topical issues affecting the environment.Although there are enough historical evidence to support the theory that climate change is a natural phenomenon,many research scientists are widely in agreement that the increase in temperature in the 20 th century is anthropologically related.The associated effects are the variability of rainfall and cyclonic patterns that are being observed globally.In Southeast Asia the link between global warming and the seasonal atmospheric flow during the monsoon seasons shows varying degree of fuzziness.This study investigates the impact of climate change on the seasonality of monsoon Asia and its effect on the variability of monsoon rainfall in Southeast Asia.The comparison of decadal variation of precipitation and temperature anomalies before the 1970 s found general increases which were mostly varying.But beyond the 1970 s,global precipitation anomalous showed increases that almost corresponded with increases in global temperature anomalies for the same period.There are frequent changes and a shift westward of the Indian summer monsoon.Although precipitation is observed to be 70%below normal levels,in some areas the topography affects the intensity of rainfall.These shifting phenomenon of other monsoon season in the region are impacting on the variability of rainfall and the onset of monsoons in Southeast Asia and is predicted to delay for 15 days the onset of the monsoon in the future.The variability of monsoon rainfall in the SEA region is observed to be decadal and the frequency and intensity of intermittent flooding of some areas during the monsoon season have serious consequences on the human,financial,infrastructure and food security of the region.

RELATIONSHIP BETWEEN THE SEASONAL TRANSITION OF EAST ASIAN MONSOON CIRCULATION AND ASIAN-PACIFIC THERMAL FIELD AND POSSIBLE MECHANISMS

The NCEP/NCAR reanalysis, CMAP rainfall and Hadley Centre sea surface temperature(SST) datasets are used to investigate the relationship between the seasonal transition of East Asian monsoon and Asian-Pacific thermal contrast, together with the possible causes. Based on the 250 h Pa air temperature over two selected key areas, the Asian-Pacific thermal difference(APTD) index is calculated. Results show that the APTD index is highly consistent with the Asian-Pacific Oscillation(APO) index defined by Zhao et al., in terms of different key areas in different seasons. Moreover, the time point of the seasonal transition of the Asian-Pacific thermal contrast can be well determined by the APTD index, indicative of seasonal variation in East Asian atmospheric circulation from winter to summer. The transition characteristic of the circulation can be summarized as follows. The continental cold high at lower tropospheric level moves eastward to the East China Sea and decreases rapidly in intensity, while the low-level northerlies turn to southerlies. At middle tropospheric level, the East Asia major trough is reduced and moves eastward. Furthermore, the subtropical high strengthens and appears near Philippines. The South Asia high shifts from the east of Philippines to the west of Indochina Peninsula, and the prevailing southerlies change into northerlies in upper troposphere. Meanwhile,both the westerly and easterly jets both jump to the north. The seasonal transition of atmospheric circulation is closely related to the thermal contrast, and the possible mechanism can be concluded as follows. Under the background of the APTD seasonal transition, the southerly wind appears firstly at lower troposphere, which triggers the ascending motion via changing vertical shear of meridional winds. The resultant latent heating accelerates the transition of heating pattern from winter to summer. The summer heating pattern can further promote the adjustment of circulation, which favors the formation and strengthening of the low-level southerly and upper-level northerly winds. As a result, the meridional circulation of the East Asian subtropical monsoon is established through a positive feedback between the circulation and thermal fields. Moreover, the time point of this seasonal transition has a significant positive correlation with the SST anomalies over the tropical central-eastern Pacific Ocean, providing a basis for the short-term climate prediction.

Reconstruction of the starting time series of rainy season in Yunnan and the evolvement of summer monsoon during 1711-1982

According to the textual research into the historical documents dominated by archives yearly, as well as the verification with several other kinds of data, the later or earlier starting time of the rainy seasons in Yunnan during 1711-1982 has been reconstructed. The analysis indicates that there are obvious fluctuations in the starting date of the rainy seasons in Yunnan in a year or years, and long fluctuation on the decadal scale. The rainy season comes earlier in the early 18th century, later in the 19th century and earlier again in the 20th century. This reflects to a certain degree the gradual change of the summer monsoon in Yunnan. There exists an obvious quasi-3 years cycle, which is related to EI-Nino＇s quasi-3 years cycle, and a 11.3-year cycle which is notably related to the 11-year cycle of the solar activity of starting date of the rainy seasons in Yunnan. Meanwhile, the dissertation finds that the EI-Nino is very important to the starting date of the rainy seasons in Yunnan. The starting date of the rainy seasons in Yunnan often comes later or normally in the year of EI-Nino. However, there is an obvious imperfect period in such influence, which in turn may mean that there is a certain fluctuation in the effect of ENSO on Asian summer monsoon.

Seasonal Transition Features of Large-Scale Moisture Transport in the Asian-Australian Monsoon Region

Using NCEP/NCAR reanalysis data for the period of 1957-2001, the climatological seasonal transition features of large-scale vertically integrated moisture transport （VIMT） in the Asian-Australian monsoon region are investigated in this paper. The basic features of the seasonal transition of VIMT from winter to summer are the establishment of the summertime ＂great moisture river＂ pattern （named the GMR pattern） and its eastward expansion, associated with a series of climatological events which occurred in some ＂key periods＂, which include the occurrence of the notable southerly VIMT over the Indochina Peninsula in mid March, the activity of the low VIMT vortex around Sri Lanka in late April, and the onset of the South China Sea summer monsoon in mid May, among others. However, during the transition from summer to winter, the characteristics are mainly exhibited by the establishment of the easterly VIMT belt located in the tropical area, accompanied by some events occurring in ＂key periods＂. Further analyses disclose a great difference between the Indian and East Asian monsoon regions when viewed from the meridional migration of the westerly VIMT during the seasonal change process, according to which the Asian monsoon region can be easily divided into two parts along the western side of the Indochina Peninsula and it may also denote different formation mechanisms between the two regions.

Structure and Propagation Characteristics of Climatological Mean Kinetic Energy of Disturbance of Intraseasonal Oscillation in Asian Summer Monsoon Zone

[Objective] The research aimed to study the structure and propagation characteristics of climatological mean kinetic energy of disturbance of intraseasonal oscillation in Asian summer monsoon zone. [Method] When South China Sea monsoon started to break out, the kinetic energy of intraseasonal oscillation disturbance in the monsoon zone was analyzed, especially the researches about the variation of South China Sea monsoon, the development of Indian monsoon and the advancement of East Asian monsoon. [Result] The developed process of Asian summer monsoon had the close relationship with the kinetic energy activity of 30-60 d low-frequency oscillation disturbance. The kinetic energy of disturbance explained the eruption, occurrence, development and termination of monsoon from the energy angle. It was found that the kinetic energy of disturbance in Arabian Sea zone, Bay of Bengal and South China Sea area was the strongest, especially in Arabian Sea zone. It illustrated that Arabian Sea zone (Somali jet) was the biggest energy source of Asian monsoon. The starting mark of monsoon eruption in the whole Asia was the abrupt eruption of South China Sea monsoon. The eruption of South China Sea monsoon in the middle dekad of May was the westward transmission result of kinetic energy of disturbance on the east sea surface of Philippines. The kinetic energy of disturbance in East Asian monsoon zone had the seasonal northward advancement in summer. The high kinetic energy center of disturbance in Indian monsoon zone changed from one to two. They were respectively in Arabian Sea and Bay of Bengal. [Conclusion] The research provided the theory basis for analyzing the atmospheric intraseasonal oscillation.

SEASONAL AND INTER-ANNUAL VARIABILITY OF THE SOUTH CHINA SEA WARM POOL AND ITS RELATION TO THE SOUTH CHINA SEA MONSOON ONSET

The South China Sea warm pool interacts vigorously with the summer monsoon which is active in the region. However, there has not been a definition concerning the former warm pool which is as specific as that for the latter. The seasonal and inter-annual variability of the South China Sea warm pool and its relations to the South China Sea monsoon onset were analyzed using Levitus and NCEP/NCAR OISST data. The results show that, the seasonal variability of the South China Sea warm pool is obvious, which is weak in winter, develops rapidly in spring, becomes strong and extensive in summer and early autumn, and quickly decays from mid-autumn. The South China Sea warm pool is 55 m in thickness in the strongest period and its axis is oriented from southwest to northeast with the main section locating along the western offshore steep slope of northern Kalimantan-Palawan Island. For the warm pools in the South China Sea, west Pacific and Indian Ocean, the oscillation, which is within the same large scale air-sea coupling system, is periodic around 5 years. There are additional oscillations of about 2.5 years and simultaneous inter-annual variations for the latter two warm pools. The intensity of the South China Sea warm pool varies by a lag of about 5 months as compared to the west Pacific one. The result also indicates that the inter-annual variation of the intensity index is closely related with the onset time of the South China Sea monsoon. When the former is persistently warmer (colder) in preceding winter and spring, the monsoon in the South China Sea usually sets in on a later (earlier) date in early summer. The relation is associated with the activity of the high pressure over the sea in early summer. An oceanic background is given for the prediction of the South China Sea summer monsoon, though the mechanism through which the warm pool and eventually the monsoon are affected remains unclear.

云南区域夏季风雨季爆发前后大气热源和云量特征

本研究应用2001~2020年欧洲中期天气预报中心第五代再分析资料(ERA5)的气象场及卫星反演的降水和云量资料,研究了云南区域夏季风雨季爆发前后大气热源和云量的气候特征。研究结果表明:(1)云南区域的大气热源和云量会受夏季风环流的强烈影响,有着明显的逐月变化。6月受来自孟加拉湾东部的西南气流水汽输送影响,云南季风雨季爆发,大气总热源(特别是降水凝结释放的潜热)和云量较4~5月明显增强,而地表感热和大气辐射冷却作用减小。(2)基于Wang and LinHo(2002)方法计算的2001~2020年期间云南夏季风雨季的平均爆发时间约为第31候,区域大气总热源(潜热)和云量均与降水呈现出高度的时间相关性,而且云南区域大气热源和云量随夏季风雨季的时间变化呈现出与相邻的南亚热带季风区相似的单峰年变化特征。(3)云南夏季风雨季爆发时间存在明显的年际变化,雨季爆发偏早(晚)年的合成结果表明:在偏早年雨季爆发时,来自孟加拉湾东南部的低层西南气流可直达云南区域,该区域上空为辐散气流,有利于区域上升运动,云南区域大气总热源(潜热)和云量明显强于偏晚年;偏晚年同时段的孟加拉湾南支槽偏弱,西太平洋副高位置明显偏西,不利于云南区域上升运动和降水。在雨季盛期,偏早和偏晚年的区域降水率接近,偏晚年的区域大气总热源(潜热)和高云量值略高于偏早年。

东亚夏季风和中国雨季的趋势变化和关键区气温和海温的影响

中国降水主要受到西风和季风环流的共同影响,表现出显著的年循环特征。本文基于1961~2020年CN05.1逐日降水资料和JRA55、CRU、HadISST再分析资料,采用谐波分析、相关和回归统计方法,分析了过去60年的东亚夏季风(中国雨季)的建立(开始)、撤退(结束)和持续时间等年循环参数趋势的变化特征。结果显示,自1961年以来,东亚夏季风有建立时间提前,撤退时间推后,持续时间增长的趋势,每十年分别达到了3.54、1.64、5.18天。1999年前后22年我国雨季也存在趋势变化,且在空间上存在显著差异。最近22年(1999~2020年),我国雨季提前主要集中在东北东部、青藏高原东部、西北北部地区,提前时间达5天以上,部分地区超过了20天。雨季滞后主要集中在青藏高原东北,长江以北和西部地区,时间超过了10天。雨季持续时间增加主要集中在青藏高原东北部、我国长江以北、东北东南部地区,时间超过15天以上,部分地区超过25天。研究发现,4月份环贝加尔湖地表气温增加及其伴随的局地反气旋性环流异常,是东亚夏季风建立和我国雨季开始时间提前的关键,而10月份的西北太平洋海温增暖及其伴随的西北太平洋副热带反气旋的异常是导致东亚夏季风撤退和中国北方雨季变长的关键。

2021年5月江西降水异常偏多特征及成因分析

2021年5月江西省降水异常偏多,多项降水指数突破历史极值,异常的降水在累计降水量、降水强度、日降水量等方面表现出极端性。利用1961—2021年江西省83站逐日降水资料和NCEP/NCAR再分析资料,分析了2021年5月江西降水异常偏多的主要原因。结果表明:5月大气环流异常是造成江西降水偏多的直接原因,欧亚中高纬500 hPa层环流呈“两脊一槽”的分布特征,受北大西洋三极子正位相影响,中国东北及周围地区位势高度为负距平,东北冷涡异常活跃,中高纬环流经向度增加,冷空气不断南下为降水提供了环流条件。西太平洋副热带高压月内加强西伸,为降水提供充足的水汽条件。此外,南海夏季风爆发偏晚和5月在印度洋活跃的热带季节内振荡对5月江西降水偏多有一定的指示意义。

德国气候预测系统中东亚冬季风的季节预测及可预报性

东亚冬季风(EAWM)作为北半球冬季最强的中纬度环流系统之一,主导着东亚的冬季气候。因此,开展东亚冬季风季节预测和可预报性研究具有十分重要的意义。本研究使用德国气候预测系统(German Climate Forecast System,简称GCFS2)输出的回报数据(1993~2016年)对EAWM的预测性能进行全面评估。GCFS2很好地预测了EAWM气候态的主要特征,包括西伯利亚高压、阿留申低压、东亚大槽、东亚高空急流及东亚上空的地表气温和降水,并可以熟练地预测东亚大槽及东亚地表气温的年际变化。GCFS2对一个海平面气压定义的EAWM指数(EAWMI)显示出了预测技巧,同时可以很好地预测与EAWM相关的位于海洋上的大气环流、地表气温及降水异常。GCFS2中EAWM的预测技巧主要得益于对观测中的EAWM–ENSO关系及ENSO遥相关的成功再现,模式中增强的EAWM–ENSO[强于观测,观测中整个24年(1993~2016)EAWM与ENSO的相关系数为-0.46]关系,有助于提前2个月或更长时间预测EAWM。GCFS2中12月初始化的EAWMI在去除ENSO信号后仍有0.42的预测技巧,说明有另一预测源,为冬季巴伦支—喀拉海区域海冰覆盖度(BK_SIC)。观测中BK_SIC减少,增强西伯利亚高压,EAWM从而增强;模式中BK_SIC的变化可以增加西伯利亚高压东北部的可预测性,使得12月初始化的EAWM预测技巧增加。

2023/2024年冬季北半球大气环流特征及对我国天气气候的影响

利用国家气象信息中心整编发布的中国台站观测资料和全球大气再分析资料,分析了2023/2024年冬季我国气候异常特征和可能成因。2023/2024年冬季,全国平均气温较常年同期偏高0.3℃,气温冷暖起伏大,总体呈现“前冬暖、后冬冷”的季节内变化特征。全国平均降水量较常年同期偏多19.8%,中东部大部地区降水偏多。东亚冬季风和西伯利亚高压强度接近常年,东亚槽偏弱。欧亚中高纬500 hPa位势高度场呈西低东高的分布形势,并具有显著的阶段性变化特征,2023年12月和2024年1月以纬向环流为主,2月转为异常经向型环流,有利于中高纬冷空气南下入侵我国。受赤道中东太平洋厄尔尼诺、热带印度洋和大西洋海温异常偏暖以及北太平洋年代际涛动负位相等因子的协同影响,冬季西太平洋副热带高压偏强、偏西,菲律宾及南海上空异常反气旋阶段性活跃,欧亚对流层高层出现沿西风急流传播的波列,有利于热带水汽向我国中东部输送,配合中高纬冷空气南下,导致该地区发生多次大范围雨雪冰冻天气过程。

The Spring Monsoon in South China and Its Relationship to Large-Scale Circulation Features

In this paper, the authors define the spring monsoon in South China, and study the climatology and the interannual variation through analysis of the precipitation and the related atmospheric circulation, as revealed by the NCEP/ NCAR reanalysis data. The results indicate that the spring monsoon season in South China occurs climatologically in April and May, which is supported by both seasonal and interannual variation of the atmospheric circulation and precipitation. The related atmospheric circulation is different from that during the East Asian summer or winter monsoon season. The interannual variation of the spring monsoon rainfall in South China relates primarily to the anomalous circulation over the North Pacific, which is linked with the westerly jet over North Asia and with the polar vortex. It is also connected with sea surface temperature anomalies in the Pacific. Changes in the Asian tropical atmospheric circulation has little influence on the spring monsoon in South China according to this research.

Seasonal Variation and Physical Properties of the Cloud System over Southeastern China Derived from Cloud Sat Products

Based on the National Centers for Environmental Prediction（NCEP） and Climate Prediction Center（CPC） Merged Analysis of Precipitation（CMAP） data and Cloud Sat products, the seasonal variations of the cloud properties, vertical occurrence frequency, and ice water content of clouds over southeastern China were investigated in this study. In the Cloud Sat data, a significant alternation in high or low cloud patterns was observed from winter to summer over southeastern China. It was found that the East Asian Summer Monsoon（EASM） circulation and its transport of moisture leads to a conditional instability, which benefits the local upward motion in summer, and thereby results in an increased amount of high cloud. The deep convective cloud centers were found to coincide well with the northward march of the EASM, while cirrus lagged slightly behind the convection center and coincided well with the outflow and meridional wind divergence of the EASM. Analysis of the radiative heating rates revealed that both the plentiful summer moisture and higher clouds are effective in destabilizing the atmosphere. Moreover, clouds heat the mid-troposphere and the cloud radiative heating is balanced by adiabatic cooling through upward motion, which causes meridional wind by the Sverdrup balance. The cloud heating–forced circulation was observed to coincide well with the EASM circulation, serving as a positive effect on EASM circulation.

Modelling the Global Monsoon System by IAP 9L AGCM

The global monsoon system is simulated by IAP 9L AGCM. The result indicates that the model successfully simulates the monsoon system in the lower troposphere including the classic tropical monsoon, the subtropical monsoon and the temperate-frigid monsoon. Besides, the planetary monsoon in the upper troposphere is also realistically reproduced. On the other hand, the stratospheric monsoon is poorly simulated, a further analysis reveals that this is caused by the systematic overestimation of the westerly in the model.