The development and dissemination characteristic of disturbance in weak tropical cyclones

Abstract

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.