热带低层弱涡旋中扰动的快速发展及其向中心传播的特征

The development and dissemination characteristic of disturbance in weak tropical cyclones

台风发生的必要条件是热带低层具有气旋式扰动,从卫星云图和诊断分析看,许多低层涡旋中存在分立的云团或中尺度系统.这些涡旋能否发展成为台风,取决于其中的中尺度波动是否发展集合组成密闭云带.本文利用柱坐标下的两层动力模式,研究了低层弱涡旋中第二类条件不稳定机制驱动下的波动的发展和移动问题.结果表明:热带弱涡旋中的低层基本流垂直切变可以很大地加强波动的不稳定性;波动的相速度和群速度都指向涡旋中心,波动向中心传播,能量向中心频散.实例和数值研究也都表明,低层涡旋中的中尺度扰动会迅速发展并且向中心靠近,促使台风形成.

The cyclone disturbance in tropical lower atmosphere is the necessary condition of typhoon forming. Satellite cloud imagery and diagnostic analysis both show that the convection represents separate cloud cluster or mesoscale systems in the disturbance. Whether these disturbances can become the typhoon depends on the strength of the convection heating in the mesoscale systems and close degree of the cloud area. This paper deals with the development and mobile of wave driven by conditional instability of second kind （CISK） mechanism through discussing frequency equation and using numerical method. The results show that the mesoscale CISK wave can occur in the tropics weak cyclone. Vertical shear of basic vortex circulation can significantly strengthen unstable effect of this wave to make fluctuation quickly develop. Vertical shear of basic vortex circulation can also make the wave move toward the center of basic vortex circulation and its group velocity points to the center too. The numerical calculation and the examples show that the disturbance will develop rapidly and move towards the center too.