Tropical cyclone: expressions for velocity components and stability parameter

Abstract

Tropical cyclones are the most devastating natural calamity forming in the ocean bed and die out in land. The life cycle of a tropical cyclone is mainly classified into four stages: (a) formation or genesis stage, (b) intensification stage, (c) mature stage and (d) decay stage. The intensification and mature stages are also known as tropical storm and cyclone (hurricane) stage, respectively. To develop the model of tropical cyclone we have taken the momentum conservation equation, equation of continuity and equation of hydrostatic balance in cylindrical coordinate system. Also the equation of state and the equation relating the velocity component and stream function are taken into account. We have assumed a suitable analytic form of the radial component of velocity as a function of radial distance (r) from the axis of the cyclone and vertical distance (z) from the sea bed. So in our model we have taken a cyclone as a rotating cylinder. With the use of the expression of the radial component velocity we have solved the governing nonlinear equation in the cylindrical coordinate system of a cyclone using ‘Wentzel–Kramers–Brillouin approximation’ and estimated the transverse velocity on the sea bed and in the vicinity of the eye wall of the cyclone. From the results we also get a path to generalize the tropical cyclone model as a vortex which is a generating curve of a cyclone. We also determine the vertical component of velocity of the cyclone. In this work we define a new parameter called the cyclone stability parameter (CSP). The CSP helps to determine the stability of a tropical cyclone from its genesis.