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

Commonly the centre of an intense heavy rain occurs in a very limited area,but for the three extraintense heavy rains of the present study,63-8 in North China,75-8 in central China and 77-8 in the desert region of Inner Mongolia,which all appeared under the environments of "Western Low and Eastern Blocking" (EB) pattern.From this study,the following effects of the EB are found:(1) It affects the precipitation systems staggering in a local place and/or changes the trajectories of low votices and urges them into the same raining areas intermittently. (2) It transports water vapour into raining areas.The air flows by the west side of EB produce strong cyclonic vorticity behind EB frequently,which transports water vapour and forms mesoscale precipitation systems more favourably than the low level jets. (3) Air flows behind EB conjugate with adequate topographic relief,which enhances the precipitation and makes the raining areas overlapped.So that extra-intense heavy rains could occur in higher latitudes of semi-aird areas,and occasionally even in the desert region of North 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 precipitation.