A Detailed Analysis of Typhoon Formation

[摘要] The formation of typhoon Doris 1958 which appeared in the Marshall Islands area is described from the stage of an easterly wave under a large high-level anticyclonic cell to the stage of an incipient vortex. It is revealed that the initial easterly wave possessed a fairly large horizontal extension of strong wind region, together with a systematic vertical motion. The formation of a thick moist layer and the variation of thermal structure of the disturbance from of a cold- to of a warm-core type are clearly shown by the analysis.Quantitative discussions of the three-dimensional distributions of vorticity, horizontal divergence and vertical velocity are made. The mechanisms of increase of vorticity at low levels, and of maintenance of negative vorticity at high levels are also discussed.The analysis reveals that the warming of ascending air was the result of liberation of latent heat of condensation. This, coupled with the cooling of surrounding air due to evaporation, created a horizontal temperature gradient of the warm-core type. The importance of the baroclinity thus formed for typhoon development may be supported by th observed fact that rapid fall of the sea-level pressure took place after the completion of the warm-core structure.Based on the results of analysis, a model of typhoon formation is described, in which the whole process of the formation is divided into three stages. Some preliminary remarks on dynamical processes in these stages are also mentioned.

[学科分类] 大气科学