ON THE INSTABILITY OF THE LOW LEVEL JET AND ITS TRIGGER FUNCTION FOR THE OCCURRENCE OF HEAVY RAIN-STORMS
Suen Shu-qing Zhai Gao-qing(Institute of Atmospheric Physics, Academia Sinica)(Department of Geography, Hangzhou University)
This is a case study of a low level jet on 2-3 July 1972, which occurred in the warm sector of a cyclone in Yantze-Hwia River basin. The heavy rain-storm occured at the left hand side of the jet. It is found that the low level jet has a characteristic three dimensional structure: to the left front quadrant side of the jet there is a region of negative Richardson number, which is the most unstable layers of the low level jet. The low level jet is strongly supergeostrophic. The heavy rain-storm occurs when the low level jet is strong enough. At the same time there are strong pulsation in wind velocity which propagate along the jet axis and trigger the meso-scale low pressure systems and rain clusters. Then, with the adaptation of the pressure field to the wind field, geostrophic balance restores, and the heavy rain ceases.