Future Changes in the Relationship Between the South and East Asian Summer Monsoons in CMIP6 Models

The future changes in the relationship between the South Asian summer monsoon (SASM) and the East Asian summer monsoon (EASM) are investigated by using the high-emissions Shared Socioeconomic Pathway 5-8.5 (SSP5- 8.5) experiments from 26 coupled models that participated in the phase 6 of the Coupled Model Intercomparison Project (CMIP6). Six models, selected based on their best performance in simulating the upper- and lower-level pathways related to the SASM-EASM teleconnection in the historical run, can capture the positive relationship between the SASM and the rainfall over northern China. In the future scenario, the upper-level teleconnection wave pattern connecting the SASM and the EASM exhibits a significant weakening trend, due to the rainfall anomalies decrease over the northern Indian Peninsula in the future. At the lower level, the western North Pacific anticyclone is projected to strengthen in the warming climate. The positive (negative) rainfall anomalies associated with positive (negative) SASM rainfall anomalies are anticipated to extend southward from northern China to the Yangtze-Huai River valley, the Korea Peninsula, and southern Japan. The connection in the lower-level pathway may be strengthened in the future.     

Impact of the thermal state of the tropical western Pacific on onset date and process of the South China Sea summer monsoon

Since the early or late onset of the South China Sea summer monsoon （SCSM） has a large impact on summer monsoon rainfall in East Asia, the mechanism and process of early or late onset of the SCSM are an worthy issue to study. In this paper, the results analyzed by using the observed data show that the onset date and process of the SCSM are closely associated with the thermal state of the tropical western Pacific in spring. When the tropical western Pacific is in a warming state in spring, the western Pacific subtropical high shifts eastward, and twin cyclones are early caused over the Bay of Bengal and Sumatra before the SCSM onset. In this case, the cyclonic circulation located over the Bay of Bengal can be early intensified and become into a strong trough. Thus, the westerly flow and convective activity can be intensified over Sumatra, the Indo-China Peninsula and the South China Sea （SCS） in mid-May. This leads to early onset of the SCSM. In contrast, when the tropical western Pacific is in a cooling state, the western Pacific subtropical high anomalously shifts westward, the twin cyclones located over the equatorial eastern Indian Ocean and Sumatra are weakened, and the twin anomaly anticyclones appear over these regions from late April to mid-May. Thus, the westerly flow and convective activity cannot be early intensified over the Indo-China Peninsula and the SCS. Only when the western Pacific subtropical high moves eastward, the weak trough located over the Bay of Bengal can be intensified and become into a strong trough, the strong southwesterly wind and convective activity can be intensified over the Indo-China Peninsula and the SCS in late May. Thus, this leads to late onset of the SCSM. Moreover, in this paper, the influencing mechanism of the thermal state of the tropical western Pacific on the SCSM onset is discussed further from the Walker circulation anomalies in the different thermal states of the tropical western Pacific.     

春季对流层温度的季内和季节以上分量对南海夏季风爆发的年代际变化的相对影响

南海夏季风爆发时间在1993/1994年出现显著的年代际提早, 探讨了大气要素场的不同时间尺度分量季节演变的年代际变异对南海夏季风爆发时间的年代际变异的相对影响作用。南海夏季风爆发时间的年代际提早与南海季风区对流层经向温度梯度季节性逆转的年代际提早有密切联系。南海季风区5月中对流层经向温度梯度年代际增强主要由季风区北部温度的年代际显著增暖造成。季内分量和季节以上分量对1993年之前南海季风区经向温度梯度逆转及加强时间偏晚的作用同等重要。经向温度梯度距平的季节以上分量主要源于季风区北部温度相应分量的贡献, 而季节内分量则主要由南部相应分量影响所致, 并由25~90 d分量所主导。季节以上分量对1994年之后南海季风区经向温度梯度逆转及加强时间偏早的贡献要大于季节内分量的贡献。经向温度梯度距平的季节以上分量和季内分量对总距平的正贡献都主要来自于季风区北部温度相应分量。两种季内低频分量对温度梯度季内分量的贡献率相当, 10~25 d分量主要由南海北部温度相应分量所主导, 25~90 d分量对总距平的正贡献也源自北部分量。准双周振荡分量对各年代南海夏季风爆发具有明显的触发作用。      

Upper- and Lower-tropospheric Circulation Anomalies Associated with Interannual Variation of Pakistan Rainfall during Summer

This study investigated the large-scale circulation anomalies, in both the upper and lower troposphere, associated with the interannual variation of rainfall in Pakistan during summer, using the station observation data in this country and circulation data of the NCEP-NCAR reanalysis from 1981 to 2017. Results showed that the upper-and lower-tropospheric circulation anomalies associated with monthly rainfall variability exhibit similar features from June to August, so analyses were performed on ...     

异常东亚冬季风激发ENSO的数值模拟研究

利用中国科学院大气物理研究所发展的热带太平洋环流模式（OGCM）和海－气耦合模式（CGCM）分别就冬半年东亚冬季风异常对赤道太平洋的作用进行了数值模拟研究。结果清楚地表明,无论在 OGCM 中还是在 CGCM 中,持续的冬季风强异常将引起赤道中东太平洋海表水温（SST）的明显正异常,其分布类似观测到的El Ni?o事件;而持续的冬季风弱异常将引起赤道中东太平洋SST的明显负异常,其分布十分类似观测到的La Ni?a事件。因此,数值模拟进一步证实了我们过去从资料诊断和理论分析中得到的结论,即东亚冬季风异常是激发产生 ENSO 的重要机制。对模式资料的分析还清楚表明,异常东亚冬季风将激发异常海洋Kelvin波和使热带大气季节内振荡出现强异常,它们是激发ENSO的重要物理因素,这与观测资料的分析结果相一致。     

地表反照率的改变影响夏季北非副热带高压的数值模拟

利用 LASG L 9R1 5AGCM设计了两组不同地表反照率的数值试验。通过分析其夏季平均气候的差异来考察地表反照率改变对夏季北非副高的影响。结果表明 ,当北非地表反照率增大时 ,由于地面接收到的净辐射减少 ,地面温度降低 ,底层大气的感热加热减弱 ,抑制了局地的对流和降水 ,相应的对流层中层的凝结加热也减弱。这种中、低层的冷却强迫出高空的异常辐合与低空的异常辐散 ,导致北非地区下沉运动增强 ,从而加强了北非副高。另外 ,这种北非地区的环流异常 ,通过辐散风环流加强了南亚高空的辐散 ,在一定程度上加强了南亚高压。     

INDIA/ASIA CONVERGENCE AND HIMALAYAN SHORTENING

INDIA/ASIA CONVERGENCE AND HIMALAYAN SHORTENING     

南海西南季风爆发日期及其影响因子

利用1950～1999年NCEP全球格点日平均资料,在总结南海西南季风爆发前后850 hPa大气环流特征的基础上,提出了一个较为客观的确定南海西南季风爆发日期的大气环流方法.在与1980～1991年其他多种指标确定的爆发日期比较后,作者认为该大气环流方法所确定的爆发日期基本合理,并给出了1950～1999年各年南海西南季风爆发的日期.通过合成对比分析和相关分析发现,前期热带太平洋地区海温异常分布是影响南海西南季风爆发早晚的重要因素.菲律宾以东洋面海温偏高,赤道太平洋中部偏东地区海温偏低,可以使低层西太平洋副高减弱、高层中东太平洋洋中槽加深,印度洋热带地区偏西风偏强,印度洋-太平洋热带地区Walker环流偏强,为热带对流在孟加拉湾-南海地区发展提供了有利的环境.在孟加拉湾南部偏西气流的作用下,南海地区对流活动较为容易发展起来,低层较弱的西太平洋副热带高压也容易较早地撤出南海上空,使得南海西南季风较早爆发.反之亦然.     

云南省典型涝夏特点及其与相关因子的关系分析

利用云南省125个气象站1961－1998年6－8月降水量资料，确定典型涝夏年，分析发生特点，并讨论其与大气环流、ENSO事件、青藏高原积雪变化及太阳黑子相对数等因子的关系，以期为云南省夏季降水趋势预测提供有意义的指示因子。     

2018年南京梅雨异常特征及环流分析

利用自动站降水数据和NCEP/NCAR再分析资料,结合江苏入、出梅指标对2018年南京梅雨进行讨论,分析导致当年南京梅雨异常的环流因子特征。结果表明：1）当年入梅偏晚、出梅正常,梅雨分布不均匀,总量偏少,其中南部异常偏少8成;2）前期南支槽活动频繁,副热带高压相比同期偏南,季节北跳偏迟,且南亚高压主体偏强,位置偏东偏北,导致入梅偏迟;3）入梅后,副热带高压大幅度北抬,南亚高压东伸明显,加之东北冷涡活动弱,使得冷暖气流交汇偏北,因此江苏沿江地区梅雨量偏少;4）南京地区的梅雨量与6-7月副热带高压的南北跨度具有显著的负相关;5）东亚夏季风偏强时,南京中北部地区的梅雨量很可能偏少。