NUMERICAL TEST OF AN EARLY-SUMMER EXPLOSIVE CYCLONE EVENT IN EAST ASIA

A series of ten numerical tests are carried out using smoothing techniques in the PSU/NACR mesoscale model MM5 initial field in order to study the development reasons of a pre-summeruncommon explosive event which took place in East Asia from 1-2 June.1993.The integration fields are compared with that of original results obtained by non-smoothed initial field.The results show that:(1)After the northern trough is smoothed,its corresponding cold air can not move downward and southward.Only a weak cyclone system forms south of 25°N after 24 h integration.(2)After the southern strong moisture transportation channel is smoothed,the northem trough system can only form a weak trough along the east coast of China after 24 h integration.(3)These two separate low trough systems in the southern and northern jet systems,with strong warm moisture transportation channel and cold air respectively,are both necessary for explosive cyclone development.In such an unfavorable season and location for explosive cyclone to take place,only after these two low troughs merged into a strong low vortex can the surface cyclone he developed explosively.Both the northern trough system and the southern moisture transportation channel are all indispensable for the explosive cyclone development.This explosive cyclone event is the result of the interaction of northern and southern systems.