THE EFFECT OF THE UPPER NORTHERLY FLOW ON THE HEAVY RAINFALL IN MEI-YU SEASON

In this paper,the features of the high and low level wind fields in the cases heavy rainfall during Mei-Yu season are analysed.The results show that,the axis of strong upper northerly flow,located on the eastside of the Qinghai-Xizang High converg into the South Asia easterly jet,plays an impontantrole in the long lastingheavy rainfall over Jiang-Huai Basin.This northerly flow enhances the upper divergence which is favorable for the development and reinforcement of low level convergence.The horizotal gradient of vertical wind shear of the vcomponent contributed to the secondary circulation between the low-level southeast jetand high-level strong northeastlies,which is responsible to the lasting of heavy rainfall during the Mei-Yu period.