高压“东阻”对特大暴雨形成的作用

BLOCKING EFFECT OF HIGH PRESSURE SYSTEM ON THE FORMATION OF EXTRA-INTENSE HEAVY RAIN

1963年8月在华北、1975年8月在华中、1977年8月在毛乌素沙漠出现的特大暴雨是我国中纬度地区近40年来最严重的三场特大暴雨。国内对它们进行过较细致的个例研究。过去,我们曾提出:在适当的地形条件下,“西低东阻”对西风带有些类型大暴雨的形成具有重要作用。本文则进一步讨论在这三场特大暴雨中,高压在低值降水系统的东部形成阻挡形势时,对特大暴雨的作用。

Commonly the centre of intense heavy rain is occurred in a very limited area, but for the three extra-intense heavy rains of present study, 63-8 in N. China, 75-8 in C. China and 77-8 in the desert region of Inner Mongolia, which are all appeared under the environments of 'Western Low and Eastern Blocking' (E. B.) pattern.1) It affects the precipitation systems stagging in a local place and/or changes the trajectories of low vortices and urges them into the same raining areas intermittently. And when the low vortex was retreated, the heaviest rainfall appeared.2) Transports water vapour into raining area in a quite thicker air column than that of low level jet. And also the air flows by the west side of E. B. produce strong cyclonic vorticity frequently, that transports water vapour and forms meso-scale precipitation systems more favorable than that of the low level jets.3) Air flows behind E. B. conjugated with the adequate topographic relief, that enchances the precipitation and makes the raining areas overlapped. Such that extra-intense heavy rains could he occurred in higher latitudes of semi-arid areas, and occasionlly even in desert region of N. China.Such extra-intense heavy rains could not be explained by static local humidity and temperature only. This is also a principal discrimination between the prolonged extra-intense heavy rain and the short-range convective precipitation and/or the common precipitations.