Numerical Simulation of Tropical Cyclone Development with the Use of Primitive Equations

摘要

Based upon arguments by Syono and Yamasaki (1966), numerical experiments for simulating the developmental process of tropical cyclones are carried out with the use of primitive equations. Thermal effects of deep cumulus clouds are incorporated in the same manner as proposed by Ooyama (1964), and Charney and Eliassen (1964). The numerical experiments are performed using a four-layer model. The effect of surface friction is included through the equations of motion applied to the lowest level. Latent heat released by cumulus clouds is distributed to two tropospheric layers, and the heat partition ratio is assumed to be timeindependent.In a case in which 57 per cents of released latent heat is given to the upper troposphere and 43 per cents to the lower one, a given weak vortex develops to the mature stage in about 8 days. The structure of the computed tropical cyclone is similar to that of observed tropical cyclones. The deviation from the gradient wind balance is notable in the upper level near the center. The ratio of kinetic energy production to released latent heat increases with time and it attains 3 per cents at the mature stage.In order to investigate the relation between the gr iwth rate (and structure) of computed tropical cyclones and various physical parameters (such as mixing ratio of water vapor of surface air q, heat partition ratio to the lower troposphere 1, static stability S, the Coriolis parameter f and the drag coefficient CD), several numerical experiments are carried out. The horizontal scale of computed tropical cyclones is decreased with decrease of the Coriolis parameter. The experiments further reveal that the growth rate of cyclones is very sensitive to the static stability of the lower layer. In a case in which 70% of released latent heat is given to the upper layer, a given vortex does not develop. The growth rate of computed tropical cyclones is increased with increase of q, l and CD.