南海夏季风建立的气候特征及其机制的讨论

Climatic Features of SCS Summer Monsoon Onset and Its Possible Mechanism

使用1998年南海季风试验期间高质量资料和NCEP/NCAR40年再分析资料分析了南海季风建立前后的大尺度环流特征和要素的突变及爆发过程。发现南亚高压迅速从菲律宾以东移到中南半岛北部,孟加拉湾槽加深加强,赤道印度洋西风加强并向东向北迅速扩展和传播,以及伴随的中低纬相互作用和西太平洋副高连续东撤是南海夏季风建立的大尺度特征。与此同时,亚洲低纬地区的南北温差和纬向风切变也发生相应的突变。数值试验结果表明,印度半岛地形的陆面加热作用在其东侧激发的气旋性环流对于孟加拉湾槽的加强有重要作用,并进而有利于南海夏季风先于印度夏季风爆发。

The high quality dataset from the SCS (South China Sea) Monsoon Experiment and 40- year NCEP/NCAR reanalysis data are used to investigate the large scale features and abrupt change in meteorological elements during the onset of the SCS summer monsoon. It is found that the large scale circulation situation favorable to the onset of the SCSSM is that the South Asian High rapidly moves from the east of Philippines to the northern Indo- China peninsula, the Bay of Bengal trough deepens and strengthens, the confluence of the westerly flow on the bottom of the trough with the equatorial westerly flow from the Southern Hemisphere forms an enhanced Equatorial Indian Ocean westerly, which then moves to the Indo- China peninsula and SCS area. The rapidly eastward and northeastward extension of westerly from the Equatorial Indian Ocean and the relevant interaction between middle and low latitude systems, and the eastward withdrawal of the West Pacific subtropical high are the characteristic processes of the onset of the SCSSM. Further study shows that the meridional temperature difference and the zonal wind vertical shear over the Asian lower latitudes also experience abrupt change during the onset of the SCS summer monsoon. Numerical results reveal that the Indian Peninsula acts as a critical role for the enhancement of the India- Burma trough with a cyclonic difference circulation excited to the east side of the peninsula through ground sensible heating in such a way that the SCS summer monsoon occurs prior to the Indian summer monsoon.