伴随南海季风爆发热带环流演变的合成分析

为了研究伴随南海夏季风爆发的热带环流的演变,利用40 a的NCEP逐日再分析资料,采用合成分析的方法对季风爆发前后的环流形势变化进行了讨论。合成结果中重点分析了随南海季风的爆发在对流层和平流层低层的流场都有显著变化的南亚、东南亚地区。结果表明,在对流层中印度洋赤道地区,在季风爆发前有东风扰动发展成为一对南北对称的低涡,随后北边的低涡演变成孟加拉湾低槽,低槽前的西南气流不断东扩,使西太副高东撤,南海季风爆发。低涡的演变和发展是影响南海季风爆发的重要因子之一。而高层的环流形势与低层不同,伴随季风爆发高层环流的演变则更多地体现出了全球尺度的特征。

Composite analysis of evolution of tropical circulation associated with summer monsoon onset in the South China Sea

With NCEP/NCAR reanalyzed data,the method of composite analysis was used to investigate the evolution of tropical circulation associated with the South China Sea summer monsoon(SCSSM) onset.The composite shows that the wind fields of troposphere and lower stratosphere over South Asia and Southeast Asia present obvious changes.It also indicates that the evolvement of a pair of cyclones over topical Indian Ocean can be regarded as an influencing factor of SCSSM onset.This couple of vortexes in troposphere,quasi-symmetric with respect to the equator,is born from a easterly perturbation before the monsoon onset.The northern vortex can finally develop into Indian-Burma trough,which causes the eastward spread of south-westerly wind,the eastward motion of Pacific high as well as the monsoon onset.Different from the variation of circulation in lower troposphere,that of upper troposphere and stratosphere shows its global-scale characteristic.