海洋性大陆西部夏季降水异常:独立和联系于IOD的模态

采用1979—2013年的NCEP/NCAR、GPCP和GODAS月平均再分析资料,通过回归分析等方法,研究了海洋性大陆(Maritime Continent,MC)地区偏印度洋一侧降水的区域性特征及其与热带、东亚地区环流变化的联系。结果表明:MC西部,爪洼岛以西洋面(A区)与苏门答腊海以西赤道洋面(B区)降水存在一定程度相关的同时,还存在较大差异。两个区域夏季降水正异常时,来自赤道印度洋、赤道太平洋、南海及孟加拉湾地区的水汽输送偏强。A区降水与IOD(Indian Ocean Diapole)现象密切相关,B区降水则与季风活动的变化联系密切。A区降水异常偏多时,混合层的暖海水向A区汇合,A区的海温异常偏高得以维持,对流层低层在A区及其西南部出现气旋性环流,产生气流辐合,有利于上升运动的发生,降水增多。当B区降水正异常时,对流层低层环流与A区降水正异常时较为相似,但气旋性环流范围偏小、偏西。B区暖海温的维持主要与海洋中的垂直运动有关。这些研究结果有利于深刻认识MC区域气候变动特征及亚洲夏季风环流异常的成因。

Summer precipitation anomaly in the western Maritime Continent: modes independent and dependent of the IOD

Influenced by many climatic factors,the precipitation anomaly over the Maritime Continent (MC) shows strong regional features.Based on the NCEP/NCAR,GPCP and GODAS monthly mean reanalysis data from the period of 1979 to 2013,in this study we investigated the regional characteristics of precipitation in the Indian Ocean side of the MC,as well as the relationships between different precipitation patterns with variations of the East Asian monsoon and tropical circulation,using regression and other statistical methods.The results show that one oceanic area to the west of Java Island (Box-A),and another in the equatorial Indian Ocean to the west of Sumatra (Box-B),are two key regions where the precipitation varies inter-annually with larger variance in the west of the MC.It is found that there are significant differences in the rainfall variation in Box-A from that in Box-B,although the rainfall variations between these two key regions are significantly correlated.When the summer precipitation is abnormally high in these two areas,the water vapor from the equatorial Indian Ocean,equatorial Pacific,South China Sea and Bay of Bengal is strong.However,precipitation in Box-A is closely related to the IOD mode,while that in Box-B has a closer relationship with monsoon activities.When the precipitation anomalies in Box-A are positive,the warm sea water in the mixed layer converges to Box-A to sustain the higher than normal SST in this area,thereby facilitating an anomalous cyclonic circulation over Box-A and its southwestern side to the Box-A in the lower troposphere.This warmer SSTA,along with the cyclonic circulation,are responsible for the anomalous upward motion and greater precipitation there.When the precipitation is abnormally high over Box-B,the anomalous circulation appears similar to that in Box-A,albeit slightly weaker and more westward.The warmer SST in Box-B is mainly related to the upwelling anomalies in the ocean.All of these results are helpful for our better understanding of the mechanisms of variations of both regional climate in the MC and the Asian summer monsoon anomalies.