水平涡度与夏季风环流变化

Horizontal Vorticity and Summer Monsoon Circulation Changes

在斜压涡度发展理论的基础上,讨论了大尺度大气运动中水平涡度向垂直涡度转化的情况,并用以刻划夏季风变动。将p坐标中涡度方程的有关项在z坐标中分离出水平涡度向垂直涡度转化的主要项,经尺度分析得出,在对流层中、高层,这些转化项中的水平分量是大尺度大气斜压性涡度发展的主要因子。通过对1998年4—8月的GAME(GEWEXAsianMonsoonExperiment,全球能量和水分循环试验(GEWEX)的子试验:亚洲季风试验,简称GAME)再分析资料进行实际计算发现,转化项在东亚夏季风上升支的600hPa及以上层次对p坐标垂直涡度的局地变化贡献很大,不能忽略。同时发现水平涡度向垂直涡度的转化对南海季风爆发和江淮梅雨入梅及其发展过程均有指示性意义。南海季风爆发以后,在中国东南部地区,转化项的大小与夏季风的活跃和中断等活动吻合,转化项的变化反映了西太平洋副高在中国大陆的活动规律。

On the basis of the theories of baroclinic vorticity development,this paper discusses the conversion of horizontal vorticity into vertical vorticity in the large-scale motion of the atmosphere,and then the conversion terms is employed to describe the evolvement of the summer monsoon.We extract the terms of horizontal vorticity conversion from the equation of vorticity in the p coordinates,which is the main component of the baroclinic vector of large-scale atmosphere in the middle-upper troposphere,and then conclude that the conversion term is able to reach the same order with that of the local variation of the vertical vorticity when the large scale precipitation takes place in the summer monsoon period in China.By analyzing and calculating the GAME reanalysis data from April to August in 1998 in the monsoon region of Chinese mainland,we also found that the conversion term is important to the large-scale cyclone developing above the 600hPa,and also indicative of the onset of the South China Sea summer monsoon(SCSSM) and the development of Jianghuai meiyu.After the onset of SCSSM,the magnitude of the conversion term is correlated with the brisk and intermittence of the summer monsoon,and its changes also reflect the movement regularity of the West Pacific subtropical high(WPSH) over the mainland.Therefore it may be a convenient way to employ the baroclinic terms in researching influence of the moist weather processes on the short-medium range change of the WPSH and the atmospheric circulations.