Concerning the Mechanism of the Decaying of Typhoon

[摘要] A quantitative analysis is made to investigate the mechanism of decaying of a tropical cyclone using the data of typhoon “Tilda” (6123).During the decaying stage of the typhoon, thermal structure of warm core at the upper layer is considerably modified. On the other hand the amount of released latent heat estimated for an air column enclosing the typhoon and extending from the surface to the top of the storm much decreases. So, this modification of the thermal field seems to be closely related to the change of activity of cumulonimbus convection within the typhoon region.It is the main purpose of the present analysis to clarify the relation between the change of the activity of convection within the typhoon region and that of warm core thermal field. For this purpose, we make a budget calculation of heat and water vapor, using the first law of thermodynamics and the continuity relation of water vapor respectively, and show that the convective transport of heat and water vapor, which has played an important role during the mature stage, weakens considerably as the typhoon decays.The later part of the analysis is devoted to determine the vertical distribution of liberation of latent heat. It is shown that the liberation of latent heat at the upper layer decreases remarkably as the thermal field is modified. This suggests that the diminution of high cumulonimbus towers which are the main source of released latent heat at the upper layer, plays an essential role on the destruction of the warm core thermal structure of the typhoon.Finally it is shown that the activity of high cumulonimbus towers is controlled by moisture supply in the lower layer.

[学科分类] 大气科学