关于亚洲夏季风爆发及北半球季节突变的物理机理的诊断分析:I季风爆发的阶段性特征

DIAGNOSTIC INVESTIGATIONS OF MECHANISM OF ONSET OF ASIAN SUMMER MONSOON AND ABRUPT SEASONAL TRANSITIONS OVER NORTHERN HEMISPHERE PART Ⅰ

该工作将亚洲季风区作为一个复杂的海－陆－气耦合系统，来深入考察季风区海－气、陆－气相互作用的基本事实和物理过程，探讨它们在决定亚洲季风爆发及北半球行星尺度大气环流的季节突变的物理机理。本文是系列文章的第一篇，着重研究亚洲夏季风爆发的区域性和阶段性特征，以及过渡季节热带、副热带地区海－气、陆－气相互作用的基本事实，初步分析了它们之间的联系。研究表明，热带季风对流于４月底到５月初越过赤道进入北半球，首先出现在孟加拉湾东部—中南半岛西南部地区，然后于５月中旬和６月上旬末分别出现在南海和印度半岛地区，呈阶段性爆发的特征。季风对流在孟加拉湾东部—中南半岛西南部地区爆发阶段，在大气环流变化和对流活动中心位置出现区别于南海季风和印度季风爆发的特征。通过对地表感热通量和海表潜热通量的分析，表明热带海洋上海表感热通量甚小于海表潜热通量，南海季风爆发时期印度洋上海表潜热通量显著增大，印度季风爆发后海表潜热通量的高值中心在孟加拉湾和阿拉伯海上建立起来。印度洋上低层增强的过赤道气流引起的强烈的海－气相互作用导致海表水汽的大量蒸发，并通过其输送作用，为季风对流的爆发提供了充足的水汽来源。过渡季节在副热带地区（沿２７．５～３７．５°Ｎ?

In this work, an sttempt had been made to explore the physical processes towards the onset of Asian summer monsoon and the abrupt seasonal transitions in a coupled ocean/land/atmosphere system.In the first paper,special attention was paid to investigate the basic facts for the establishment of Asian summer monsoon and the atmosphere/ocean/land interactions over the tropics and subtropics.It is shown that the Asian summer monsoon system underwent three distinct stages of the onset in the early May,middle May and middle June, resulting in deep convection and intensive rainfall over the southwestern coast of Indo China, the South China Sea and the southern Indian subcontinent respectively.When the monsoon convection burst out over South China Sea,the maximum centre of the surface latent heat flux(LHF)in relation to the development of the cross equatorial flows moved northward from the southern equatorial Indian Ocean, and two intense maximun centres of LHF appeared over Arabian Sea and the Bay of Bengal when monsoon rainfall bust out over southern Indian subcontinent.At meantime land sea contrast of LHF became distinct over the eastern coast of Africa.In the subtropical middle latitude of 25 7-37 5°N from winter to summer months, the LHF and surface sensible heat flux(SHF)intensified gradually over the Tibetan Plateau whereas decreased over west Pacific. It should be noticed that the air sea interaction play an important role during the onset of monsoon rainfall:it resulted in the intense evaporation and then transported the water vapour to the areas where strong convection bust out.