2012年载人航天主着陆场区极端降水事件的形成机制

The Formation Mechanism of an Extreme Precipitation Event on The Main Landing Field During 2012

利用卫星资料、航天主着陆场区观探测资料和NCEP的1°×1°再分析资料,对场区2012年6月一次极端降水事件进行研究。结果表明:极端降水是在异常偏强的冷、暖空气交汇对峙过程中产生的;500 hPa为贝加尔湖低涡东南部西南气流,850 hPa为东北—西南向冷切变,高空构成北槽南涡形势,地面由前期冷锋演变为后期地面倒槽;大气高温高湿,中层对流不稳定;异常偏强的冷空气来自北方,从底层楔入,一方面与暖湿空气汇合产生辐合上升,另一方面抬升暖湿气流,使上升运动加剧,降水增加。由于暖湿气流势力偏强,冷空气在南下过程中减弱变性,移速减慢,鄂霍次克海阻塞高压脊稳定少动,促使冷暖空气在场区对峙时间延长,异常降水事件出现。

Based on the satellite imagery, surface observation data, sounding data and NCEP reanalysis data （resolution 1°×1°）, the large-scale persistent severe precipitation on the main landing field from 25 to 28 June 2012 is analyzed. Results show that the severe precipitation occurred when the cold air met southwestly warm and humid air. There was southwest current ahead of the trough at 500 hPa and the northeast-southwest shear line at the 850 hPa. The surface cold front turned to ground trough. The temperature and humidity of atmosphere were high with convective instability. The invasion of severe cold air took place in the lower levels. The cold air met warm, damp air so as to form the convergence and updraft meanwhile the ascending movement of the warm, damp air was strengthened and the precipitation increased. Owing to the severe warm and damp currents, the cold air weakened during moving southward and the velocity slowed down. The Okhotsk blocking ridge was dynamically stabile so that the cold air and warm air confronted each other for a long time in the lower reaches of the main landing field, therefore, the severe precipitation maintained persistently leading to an abnormal precipitation event.