A Diagnostic Study of the Composite Ambient Fields of the Explosively Developing Typhoons
爆发性发展台风合成环境场的诊断分析

The ambient fields in the smooth evolution stage are compared with the explosively developing stage of the composite typhoon composited by 5 typhoons. The results show that in the explosively developing stage, the sub-tropical high and its anti-cyclone circulation are intensified. The low level wind to the east of typhoon increases. The upper air easterly wind disturbace overlays on the typhoon. The low level convergence and high level divergence, and the low level moisture flux convergence, the low level vertical circulation and the convective instability in the ambient field of typhoon are all intensified significantly. The above factors result in cumulus convection development. In the weak vertical shear environment, the conditional instability of the second kind (CISK) mechanism causes the rapid decrease of pressure in typhoon center and significant increase of the cyclonic circulation, so that the explosively developing typhoon may result from the interaction between the large-scale motion and cumulus convections.