连晴和连阴雨前两支气流变化的一般特点

FEATURES OF TWO FLOWS PRIOR TO SUSTAINED FINE PERIODS OR OVERCAST-WITH-RAINY PERIODS

本文使用10次连晴和7次连阴雨天气过程合成资料,分析了长江中下游春季连晴和连阴雨前700hPa 的流场及青藏高原东北侧和东南侧两支气流变化的一般特点。结果发现,连晴前,高原东侧纬向气流较弱,北支气流向南扩展,使高原东侧的流场变成连晴时的经向型;连阴雨前,高原东侧有较强的纬向气流,南支气流向北扩展,是造成连阴雨时两支气流相向运动较强的主要原因。

Based on the data about 10 cases of sustained fine periods and 7 cases of sustained overcast-with-rainy periods in spring time 1980—1986 in the middel and lower reaches of ChangjiangRiver,the features are analysed of 700 hPa streamline fields and of the two flows northeast andsoutheast of the Qinghai Xizang Plateau.It is found that prior to sustained fine periods,the zonalflow east of the Plateau is weaker,and the north branch flow spreads southward,thus forming themeridional streamline field and initiating the sustained fine periods.Prior to sustained overcast-with-rainy periods,the zonal flow east of the plateau is stronger,and the south branch flowspreads northward.This is the reason why the stronger interfacing motion occurs between the twoflows during the sustained overcast-with-rainy periods.