索马里急流与我国西南地区5月降水的联系及其年代际变化

利用1951~2010年的NECP/NCAR再分析资料和GPCC(Global Precipitation Climatology Centre)降水资料,分析了索马里急流强度与西南降水的联系。研究结果表明:索马里急流与西南降水在初夏5月有很好的正相关关系,当索马里急流偏强时,西南地区降水偏多;反之,索马里急流偏弱时,西南地区降水偏少。进一步的分析发现,两者的联系存在明显的年代际变化,事实上,西南地区5月降水与索马里急流之间的关系在1980年代以后显著加强。低层风场辐合是西南地区5月降水的关键环流配置特征,在1980年之前,5月索马里急流强度仅仅与从孟加拉湾到我国东部地区的低层西南风场相关;但在1980年之后,其与我国西南地区以西的西南风和其以东的东北风均有密切的联系。索马里急流强度与中国西南初夏降水关系的加强,主要是由于索马里急流作用的东伸加强,这可能与印度洋对东亚季风影响作用的加强有关。

The Relationship between Somali Jet and Rainfall in May over Southwest China and Its Decadal Variability

Based on the NCEP/NCAR reanalysis product and GPCC (Global Precipitation Climatology Centre) rainfall data, the relationship between Somali Jet intensity and rainfall over Southwest China is investigated in this study. The results reveal that rainfall in the early summer (May) over Southwest China is closely related to Somali Jet intensity. When the Somali Jet is stronger than normal, the May rainfall over Southwest China is larger than normal, and vice versa. Further studies show an obvious decadal variation in the relationship. In fact, the stable relationship between the Somali Jet intensity and May rainfall over Southwest China has been established since the 1980s. The convergence of wind fields at low levels in the atmosphere is a key general circulation pattern for the May rainfall over Southwest China. Before 1980, the Somali Jet intensity was only related to southwesterlies over the region from the Bay of Bengal to southern China. However, it is closely related not only to southwesterly flows to the west of Southwest China but also to northeasterly flows to the east of Southwest China after 1980. This is a possible reason for the establishment of the relationship between Somali Jet intensity and May rainfall over Southwest China.