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

Vertical structure of summer Somali cross-equatorial flow and its relationship with South Asian monsoon

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。

Based on the monthly NCEP/NCAR reanalysis wind field data from 1950 to 2009, the vertical structure variation of summer Somali cross-equatorial flow and its relationship with South Asian summer monsoon are analyzed. Results show that summer Somali cross-equatorial flow increases firstly at low level in vertical direction, then it gradually weakens after reaching maximum at 925 hPa. The height of Somali cross-equatorial flow core can extend to 850 hPa in some years, while maintains at 925 hPa in some other years. The South Asian summer monsoon is different with the vertical structure of Somali cross-equatorial flow changes, and the difference mainly embodies variation of lower troposphere wind field and the intensity difference of South Asian summer monsoon. In general, South Asian summer mon- soon becomes strong（weak） when Somali cross-equatorial flow core extends to 850 hPa（lies at 925 hPa）.