高空急流加速与低层锋生

THE LOWER LAYER FRONTOGENESIS INDUCED BY THE ACCELERATION OF UPPER JET STREAM

本文从动力学上找到了低层锋生函数同急流区内纬向平均风加速的关系,指出高空急流加速有利于大气低层锋生,并从天气学的角度给出了高空急流加速同低层大气锋生的环流形态特征。即高空波的动量和热量通量在急流区的辐合,促使高空急流加速,并引起急流入口区上下层之间的质量调整,在急流轴高度以下出现一个反环流,反环流的上升支同其下原有的弱锋前的上滑爬升气流发生耦合,造成上滑气流加强,低层锋面坡度变陡,冷暖对比明显,引起大气低层锋生。

This paper gives the relation between the lower layer frontogenesis function and mean-flow acceleration in the region of the upper jet stream, and indicates that the lower layer frontogenesis is induced by the acceleration of upper jet stream. Further, the secondary circulation characteristics of the lower layer frontogenesis induced by the acceleration of upper jet stream are described from weather analysis point of view. That is, momentum and heat fluxes of upper transient waves converge into the region of upper jet stream, then the convergence of these fluxes make both mean-flow and upper jet stream accelerations. The acceleration induces the mass adjustment between upper layer and lower layer at the entrance region of upper jet stream. Below upper jet stream, a secondary inverse circulation forms because of the mass adjustment. The ascending branch of the secondary circulation couples the climbing current along preceding weaker front in the lower layer. The couple promotes enhancement of climbing current and makes precipitous front slop and comparison between cold air and warm air more evident than before. As a result, frontogenesis in the lower layer of atmosphere occurs.