LARGE SCALE ENVIRONMENTAL CONDITIONS FOR THUNDERSTORM DEVELOPMENT

The large-scale environmental conditions for thunderstorm development have been studied with 40 selected synoptic processes during 1972-1983. It is shown that the thunderstorms in eastern China can be divided into two types: pre-trough and post-trough. The convective instability before the pre-trough thunderstorms is established primarily by the dry and moist differential advection and that before the post-trough thunderstorms by the cold and warm differential advection. The subsynoptic scale circulation has direct effects on the establishment and release of instability. The pre-trough thunderstorms occur in the overlapping region of the ascending motion in the upper baroclinic waves and the ascending branch of the low-level jet strong wind core circulation and the post-trough thunderstorms occur in the lower convergent region below the ascending branch of the jet-front circulation. The effect of the lower dry and warm lids, the coupling of the low-and upper-level jets and the dry advection in the middle-level jet are the favorable factors for the severe storm formation.