东亚和南亚季风协同作用对西南地区夏季降水的影响

为探究东亚夏季风(EASM,East?Asian?summer?monsoon)和南亚夏季风(SASM,South?Asian?summer?monsoon)相互作用及其强弱变化对西南地区夏季降水的影响,利用1979—2019年西南地区161站逐日降水观测资料和ERA-5提供的1979—2019年全球再分析资料,通过对...     

Revisiting the linear instability view of the South Asian monsoon onset

Theoretical and Applied Climatology - The mechanisms of the onset of the South Asian monsoon (SAM) remain unclear due to its abruptness and significant year-to-year spatiotemporal variations. This...     

南亚和东亚热带夏季风强弱不同配置及其对中国夏季降水的影响北大核心

利用NOAA向外长波辐射(OLR)、NCEP/NCAR再分析资料和CN05.1降水资料,研究了南亚和东亚热带夏季风强度年际变化关系,及其强弱不同配置对中国夏季降水的影响。结果表明:南亚和东亚热带夏季风强度变化之间存在同相和反相两种配置,定义的强度同相和反相变化指数可以很好地表征该关系。同相变化模态可能与海温异常时的强El Nino(La Nina)影响有关,其反相变化模态受El Nino(La Nina)以及印度洋海盆一致模的影响,同时西太平洋副热带高压和伊朗高压位置东西偏移和强度变化也影响着不同配置的出现。两者不同配置时,对中国夏季降水的影响不同。当变化呈同相偏强时,夏季中国东部地区降水为“中间少南北多”的雨型。当变化呈反相,东亚热带夏季风偏强南亚夏季风偏弱时,夏季中国东部地区降水为“一致偏少”雨型。     

Non-uniform spatial difference in the South Asian summer monsoon during the mid-Piacenzian

利用CAM4模拟研究了上新世暖期(3.264–3.025 Ma)相对工业革命前南亚夏季风的差异。模拟结果显示,上新世暖期相对工业革命前,南亚夏季风表现出不均一的空间差异。在~20°N以北,上新世暖期南亚夏季降水更多且西南风更强,而在~20°N以南降水减少并伴有异常的东风。这些差异与两个时期边界条件改变所引起的海表面气压的差异有关。进一步分析发现,两个时期大气CO_2含量和海表温度的差异是导致南亚夏季风差异的主要原因。通过对比发现,模拟得到的上新世暖期印度半岛北部的湿润气候与地质证据定性一致。     

Projected changes in South Asian summer monsoon by multi-model global warming experiments

South Asian summer monsoon (June through September) rainfall simulation and its potential future changes are evaluated in a multi-model ensemble of global coupled climate models outputs under World Climate Research Program Coupled Model Intercomparison Project (WCRP CMIP3) dataset. The response of South Asian summer monsoon to a transient increase in future anthropogenic radiative forcing is investigated for two time slices, middle (2031–2050) and end of the twenty-first century (2081–2100), in the non-mitigated Special Report on Emission Scenarios B1, A1B and A2 .There is large inter-model variability in the simulation of spatial characteristics of seasonal monsoon precipitation. Ten out of the 25 models are able to simulate space–time characteristics of the South Asian monsoon precipitation reasonably well. The response of these selected ten models has been examined for projected changes in seasonal monsoon rainfall. The multi-model ensemble of these ten models projects a significant increase in monsoon precipitation with global warming. The substantial increase in precipitation is observed over western equatorial Indian Ocean and southern parts of India. However, the monsoon circulation weakens significantly under all the three climate change experiments. Possible mechanisms for the projected increase in precipitation and for precipitation–wind paradox have been discussed. The surface temperature over Asian landmass increases in pre-monsoon months due to global warming and heat low over northwest India intensifies. The dipole snow configuration over Eurasian continent strengthens in warmer atmosphere, which is conducive for the enhancement in precipitation over Indian landmass. No notable changes have been projected in the El Niño–Monsoon relationship, which is useful for predicting interannual variations of the monsoon.     

Daily modes of South Asian summer monsoon variability in the NCEP climate forecast system

The leading modes of daily variability of the Indian summer monsoon in the climate forecast system (CFS), a coupled general circulation model, of the National Centers for Environmental Predictions (NCEP) are examined. The space?Ctime structures of the daily modes are obtained by applying multi-channel singular spectrum analysis (MSSA) on the daily anomalies of rainfall. Relations of the daily modes to intraseasonal and interannual variability of the monsoon are investigated. The CFS has three intraseasonal oscillations with periods around 106, 57 and 30?days with a combined variance of 7%. The 106-day mode has spatial structure and propagation features similar to the northeastward propagating 45-day mode in the observations except for its longer period. The 57-day mode, despite being in the same time scale as of the observations has poor eastward propagation. The 30-day mode is northwestward propagating and is similar to its observational counterpart. The 106-day mode is specific to the model and should not be mistaken for a new scale of variability in observations. The dominant interannual signal is related to El Ni?o-Southern Oscillation (ENSO), and, unlike in the observations, has maximum variance in the eastern equatorial Indian Ocean. Although the Indian Ocean Dipole (IOD) mode was not obtained as a separate mode in the rainfall, the ENSO signal has good correlations with the dipole variability, which, therefore, indicates the dominance of ENSO in the model. The interannual variability is largely determined by the ENSO signal over the regions where it has maximum variance. The interannual variability of the intraseasonal oscillations is smaller in comparison.     

Mechanism of ENSO influence on the South Asian monsoon rainfall in global model simulations

Theoretical and Applied Climatology - Coupled ocean atmosphere global climate models are increasingly being used for seasonal scale simulation of the South Asian monsoon. In these models, sea...     

A climatological study on the role of the South China Sea monsoon onset in the development of the East Asian summer monsoon

The unique role of the South China Sea summer monsoon (SCSSM) onset process in the development of the East Asian summer monsoon (EASM) is demonstrated in this study. The SCSSM onset process is examined in terms of the vertical linkage between the Western Pacific subtropical high (WPSH) and the South Asian high (SAH). A composite analysis is performed in order to adequately describe the vertical linkage in a synoptic timescale. The South China Sea (SCS) is a key region for the seasonal migrations of the WPSH and the SAH, with the former retreating northeastward, the latter advancing northwestward, and both taking place over the SCS during the SCSSM onset period. The SCSSM onset process is characterized by a significant change in the relative configuration of the ridge lines of the WPSH and the SAH. Just prior to the onset period, the ridge lines intersect vertically over the SCS, thus prohibiting convective activities. During the onset period, the ridge line intersection moves away from the SCS due to the retreating WPSH and the northward shift of the SAH ridge line. This coincides with the emergence of monsoonal convective activities over the SCS and the establishment of a moisture channel from the tropics, which in turn provides favorable conditions for the development of deep convective activity. The northeastward intrusion of the lower level southwesterlies and the moisture supplying channel are closely related to the development of a preexisting twin cyclone in the Bay of Bengal. The northeastward lower level southwesterlies form a monsoonal ascending motion in the SCS, which further merges upward into the northeasterlies to the south of the SAH ridge line. This is a signature of the establishment of the local Hadley circulation, which marks the beginning of the EASM. The frontal system is the most frequent attendant synoptic event during the SCSSM onset. From the viewpoint of synoptic process, the SCSSM undergoes a two-stage onset process which is characterized by the southward intrusion of the frontal system in the earlier stage and the outbreak of the tropical convection in the later stage. The frontal system may act as a trigger for the outbreak of the tropical convection in the later stage. The burst out of the monsoonal convection over the SCS is essential for the breakdown of the vertical intersection between the WPSH and the SAH therein.     

东亚季风区的季风类型

从地面流场正、斜压分量的冬夏季节转换的特征 ,对东亚至西太平洋季风区季风的性质进行了分析研究。结果表明 :这一地区的季风可分为 3种类型 :南海、华南沿海和低纬西太平洋主要为斜压流型季风区 ;华北北部、东北地区沿海主要为正压流型季风区 ;我国东部沿海和长江流域以及 2 7°N附近的西太平洋地区为正斜压流型共同形成的混合型季风区。     

夏季索马里越赤道气流垂直结构特征及其与南亚夏季风的关系

采用1950-2009年NCEP/NCAR月平均再分析风场资料,对夏季低空索马里越赤道气流的垂直结构及其与南亚夏季风的关系进行研究.结果表明:夏季索马里越赤道气流在垂直方向上从低层至高层先增强,在925 hPa高度上达到最大值后逐渐减弱.某些年份索马里越赤道气流核心可向上延伸至850 hPa高度,而某些年份则维持在925 hPa高度上.索马里越赤道气流垂直结构不同时,其对应的南亚夏季风也有所不同,这种差异主要体现在对流层低层风场的变化,以及南亚夏季风的强弱差异方面.总体来说,索马里急流核心高度延伸至850 hPa时,对应的南亚夏季风偏强;急流核心高度维持在925 hPa时,南亚夏季风偏弱.     

High resolution simulation of the South Asian monsoon using a variable resolution global climate model

This study examines the feasibility of using a variable resolution global general circulation model (GCM), with telescopic zooming and enhanced resolution (~35 km) over South Asia, to better understand regional aspects of the South Asian monsoon rainfall distribution and the interactions between monsoon circulation and precipitation. For this purpose, two sets of ten member realizations are produced with and without zooming using the LMDZ (Laboratoire Meteorologie Dynamique and Z stands for zoom) GCM. The simulations without zoom correspond to a uniform 1° × 1° grid with the same total number of grid points as in the zoom version. So the grid of the zoomed simulations is finer inside the region of interest but coarser outside. The use of these finer and coarser resolution ensemble members allows us to examine the impact of resolution on the overall quality of the simulated regional monsoon fields. It is found that the monsoon simulation with high-resolution zooming greatly improves the representation of the southwesterly monsoon flow and the heavy precipitation along the narrow orography of the Western Ghats, the northeastern mountain slopes and northern Bay of Bengal (BOB). A realistic Monsoon Trough (MT) is also noticed in the zoomed simulation, together with remarkable improvements in representing the associated precipitation and circulation features, as well as the large-scale organization of meso-scale convective systems over the MT region. Additionally, a more reasonable simulation of the monsoon synoptic disturbances (lows and disturbances) along the MT is noted in the high-resolution zoomed simulation. On the other hand, the no-zoom version has limitations in capturing the depressions and their movement, so that the MT zone is relatively dry in this case. Overall, the results from this work demonstrate the usefulness of the high-resolution variable resolution LMDZ model in realistically capturing the interactions among the monsoon large-scale dynamics, the synoptic systems and the meso-scale convective systems, which are essential elements of the South Asian monsoon system.     

Modelling the Asian summer monsoon using CCAM

A ten-year mean (1989–1998) climatology of the Asian summer monsoon is studied using the CSIRO Conformal-Cubic Atmospheric Model (CCAM) to downscale NCEP reanalyses. The aim of the current study is to validate the model results against previous work on this topic, in order to identify model strengths and weaknesses in simulating the Asian summer monsoon. The model results are compared with available observations and are presented in two parts. In the first part, the mean summer rainfall, maximum and minimum temperatures and winds are compared with the observations. The second part focuses on validation of the monsoon onset. The model captures the mean characteristics such as the cross-equatorial flow of low-level winds over the Indian Ocean and near the Somali coast, rainfall patterns, onset indices, northward movements, active-break and revival periods.     

关于东亚副热带季风若干问题的讨论

利用NCEP/NCAR再分析格点资料、TRMM卫星降水资料、中国东部站点降水资料和CMAP降水资料,重点讨论了东亚副热带季风雨季的起始时间、建立特征及其和南海夏季风的关系,同时也讨论了东亚副热带季风的可能机制。结果表明：（1）东亚副热带季风雨季于3月底—4月初（第16—18候）在江南南部和华南北部首先开始,伴随着降水的开始是偏南风的增强和对流性降水的显著增加,华南前汛期开始。（2）东亚副热带季风雨季的建立早于热带季风雨季,在热带季风建立后两者的雨带、强西南风带、强垂直运动带、强低空水汽辐合带均是分离的,南海热带季风在其建立后,与东亚副热带季风发生相互作用,促使副热带季风雨带季节性北进,两者共同影响中国的旱涝。（3）3月中下旬,东亚大陆（包括青藏高原）上空大气由冷源转为热源,东亚大陆与西太平洋之间的纬向热力差异及其相应的温度和气压对比均发生反转。东亚大陆（包括青藏高原）的动力和热力作用究竟是否是东亚副热带季风雨带提前建立的机制值得进一步研究。文章最后讨论了有关东亚副热带季风的共识与分歧。     

The summer circulation over the eastern Mediterranean and the Middle East: influence of the South Asian monsoon

The summer circulation over the eastern Mediterranean and the Middle East (EMME) is dominated by persistent northerly winds (Etesians) whose ventilating effect counteracts the adiabatic warming induced by large scale subsidence. The ERA40 dataset is used to study the vertical distribution of these circulation features, which both appear to be reconciled manifestations of the South Asian monsoon influence. As predicted by past idealized modeling studies, in late spring a westward expanding upper level warm structure and subsidence areas are associated with Rossby waves excited by the monsoon convection. Steep sloping isentropes that develop over the EMME facilitate further subsidence on the western and northern periphery of the warm structure, which is exposed to the midlatitude westerlies. The northerly flow and descent over the eastern Mediterranean have maxima in July that are strikingly synchronous to the monsoon convection over northern India, where the weaker easterly jet favors a stronger Rossby wave response and consequent impact on the EMME circulation. The pronounced EMME topography modifies the monsoon induced structure, firstly, by inducing orographically locked summer anticyclones. These enhance the mid and low level northwesterly flow at their eastern flanks, leading to distinct subsidence maxima over the eastern Mediterranean and Iran. Secondly, topography amplifies the subsidence and the northerly flow over the Aegean, Red Sea, the Iraq—Gulf region and to the east of the Caspian Sea.     

Vertical structures of atmospheric properties in Southeast Tibet during the South Asian summer monsoon in 2013

In June 2013, a field experiment was conducted in Southeast Tibet in which the air temperature, moisture, and wind were measured by using a GPS sounding system. In the present study, based on these observations and ERA-Interim reanalysis data, the vertical structures of these atmospheric properties and the possible influence of the South Asian summer monsoon (SASM) were investigated. On average, the temperature had a lapse rate of 6.8℃km^?1 below the tropopause of 18.0 km. A strong moisture inversion occurred at the near-surface, with a strength of 1.7 g kg^?1 (100 m)^?1 for specific humidity. During the observation period, the SASM experienced a south phase and a north phase in the middle and by the end of June, respectively. The monsoon’s evolution led to large changes in convection and circulation over Southeast Tibet, which further affected the local thermal, moisture, and circulation conditions. The strong convection resulted in an elevated tropopause height over Southeast Tibet during the north phase of the SASM, and the large-scale warm and wet air masses delivered by the monsoon caused high local temperature and moisture conditions.     

青藏高原与印度洋热力对比及其与南亚夏季风的关系

本文基于1979-2017年逐日再分析资料,通过分析对流层中上层青藏高原和印度洋之间的热力差异,提出了一个热力对比指数(TCI),并分析了TCI与南亚夏季风的强度和爆发时间的关系.研究表明:相比单独的青藏高原或者印度洋的温度,TCI能更好地表示南亚夏季风强度的变化.TCI越大时,南亚夏季风爆发时间越早;TCI逐候增量的...     

热带西太平洋夏季风和南海夏季风之间的联系

根据热带西太平洋（１３０°－１６０°Ｅ,１０°－２０°Ｎ）上空对流的年际变化,对表面温度、向外长波幅射、８５０ ｈＰａ纬向风进行了合成分析。合成分析结果表明,热带西太平洋上空的弱（强）对流对应着前冬和春季厄尔尼诺（拉尼娜）型的海温异常。与以前的研究结果进行了比较,说明上述海温异常的时空分布也与热带西太平洋和南海季风的爆发早晚相关联。合成分析结果还表明,热带西太平洋上空的弱（强）对流对应着从热带西太平洋向西伸展到盂加拉湾的东风（西风）异常。数值模拟也得到类似的结果。此外,在对流弱（强）的夏季,热带西太平洋上空的对流和南海低层纬向风均表现出弱（强）的季节演变特征。     

Impact of Indian summer monsoon on the South Asian High and its influence on summer rainfall over China

By using the monthly ERA-40 reanalysis data and observed rainfall data, we investigated the effect of the Indian summer monsoon (ISM) on the South Asian High (SAH) at 200 hPa, and the role played by the SAH in summer rainfall variation over China. It is found that in the interannual timescale the east–west shift is a prominent feature of the SAH, with its center either over the Iranian Plateau or over the Tibetan Plateau. When the ISM is stronger (weaker) than normal, the SAH shifts westward (eastward) to the Iranian Plateau (Tibetan Plateau). The east–west position of SAH has close relation to the summer rainfall over China. A westward (eastward) location of SAH corresponds to less (more) rainfall in the Yangtze-Huai River Valley and more (less) rainfall in North China and South China. A possible physical process that the ISM affects the summer rainfall over China via the SAH is proposed. A stronger (weaker) ISM associated with more (less) rainfall over India corresponds to more (less) condensation heat release and anomalous heating (cooling) in the upper troposphere over the northern Indian peninsula. The anomalous heating (cooling) stimulates positive (negative) height anomalies to its northwest and negative (positive) height anomalies to its northeast in the upper troposphere, causing a westward (eastward) shift of the SAH with its center over the Iranian Plateau (Tibetan Plateau). As a result, an anomalous cyclone (anticyclone) is formed over the eastern Tibetan Plateau and eastern China in the upper troposphere. The anomalous vertical motions in association with the circulation anomalies are responsible for the rainfall anomalies over China. Our present study reveals that the SAH may play an important role in the effect of ISM on the East Asian summer monsoon.