A NUMERICAL EXPERIMENT ON THE DEVELOPMENT OF A TROPICAL CYCLONE

Akira Kasahara The University of Chicago

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Abstract

A model of a tropical cyclone is constructed which is based upon conservation of momentum, mass,water vapor and heat in the hydrostatic system. The horizontal and vertical eddy-exchange processes for momentum, moisture and heat are included in the equations in order to incorporate the planetary frictional (Ekman) layer into the model. The effects of the surface boundary (Prandtl) layer are simulated by the boundary conditions for the equations, which permit the evaluation of surface stress, the sensible heat transport and the evaporation of water vapor from the earth surface. The energy sources of the model are the latent heat of condensation released during the ascent of moist air and the sensible heat transported from the ocean surface.

The formulation of the finite-difference equations for the axially-symmetric case is presented, together with an examination of the computational stability. By means of a high-speed computer, two independent computations with and without the supply of latent heat were made from the same initial wind and temperature fields.

A comparison of the two cases reveals an important effect of latent heat of condensation upon the development of the tangential motion as well as its warm-core radial circulation. It is shown that the formation of cellar convective bands in the system is a manifestation of the gravitational instability which does not occur without the latent-heat supply.

Abstract

A model of a tropical cyclone is constructed which is based upon conservation of momentum, mass,water vapor and heat in the hydrostatic system. The horizontal and vertical eddy-exchange processes for momentum, moisture and heat are included in the equations in order to incorporate the planetary frictional (Ekman) layer into the model. The effects of the surface boundary (Prandtl) layer are simulated by the boundary conditions for the equations, which permit the evaluation of surface stress, the sensible heat transport and the evaporation of water vapor from the earth surface. The energy sources of the model are the latent heat of condensation released during the ascent of moist air and the sensible heat transported from the ocean surface.

The formulation of the finite-difference equations for the axially-symmetric case is presented, together with an examination of the computational stability. By means of a high-speed computer, two independent computations with and without the supply of latent heat were made from the same initial wind and temperature fields.

A comparison of the two cases reveals an important effect of latent heat of condensation upon the development of the tangential motion as well as its warm-core radial circulation. It is shown that the formation of cellar convective bands in the system is a manifestation of the gravitational instability which does not occur without the latent-heat supply.

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