On the Formation of Tropical Cyclones

Abstract

In the present paper, an attempt is made to obtain dynamically the criterion for formation of tropical cyclones. Main factors important for typhogenesis are vertical thermal instability, horizontal dynamical stability, horizontal and vertical dimensions of perturbations. First the physical picture of a typhogenetical process is given. Secondly a method which enables us to treat the latent instability dynamically, a polytropic change method, is proposed. Thirdly using this method, the perturbation equations for the perturbations of typhoon-type are obtained. Solving these equations, the following criterion for the development of perturbations of typhoon-type is obtainedwhere g, S, Z. n and r0 are gravity acceleration, vertical thermal instability, absolute vorticity, number of loops of perturbations in vertical direction and number which gives horizontal dimension of perturbations in 100 km. The left hand side has a similar form as Richardson number for the formation of turbulence. Fourthly, modes of perturbations are investigated.