北部湾热带低压发展成台风的结构演变和动能收支的诊断分析

本文对1985年8月下旬北部湾热带低压发展为台风的演变过程作了诊断分析。发现在台风的生成和加强的过程中,涡旋动能出现显著的加强和向下转移,最大涡度层和无辐散层明显下降.与此同时,暖心结构也逐步形成。这一过程与低层西南季风的增强北进,卷入台风环流中的过程密切相关。涡旋动能收支的计算表明,低压由于处在强的水平切变和垂直切变基流中,风场和温度场的不对称和暖心结构的形成,使台风获得正压和斜压不稳定能量,加之以积云对流为代表的次网格过程向涡旋运动输送能量,从而使低压发展为台风。台风的衰亡是由于登陆后低层偏冷气流的入侵和下部暖心结构的破坏,使台风只有纬向平均气流取得能量,不足以补偿摩擦耗散和位能通量的辐散,因而减弱为低压的。 

AN ANALYSIS OF STRUCTURE EVOLUTION AND KINETIC ENERGY BUDGET DURING A TROPICAL DEPRESSION INTENSIFICATION INTO A STORM IN THE BEIBU BAY

In this paper, a synoptic analysis is made for the evolution process of a tropi cal depression intensification into a storm in the Beibu Bay during August 1985. It could be seen that the eddy kinetic energy was increasing and the levels of maximal vorticity and non-divergence were descending, and that the thermodyna mic structure with a warm core was forming gradually associating with the SW Monsoon in lower troposphere, which was strengthening and moving northward with its currents entrained into the storm, during the periods of initiation and intensification of the storm.The calculation of the budget of eddy kinetic energy is made for the storm Because the storm located in a mean flow with strong horizontal and vertical shear and its wind field and temperature distribution were asymmetric and because the storm had a warm core, the storm could develop from a depression by means of obtaining barotropic and baroclinic energy. Moveover, subgrid-scale processes represented by cumulus convection were providing energy for the storm.Because of the storm’ s warm core being destroyed by the colder air invading at low layer; the energy which the storm received from the mean flow couid not make enough compensation for the loss due to friction and flux divergence of geopotential energy, and the storm fell into decay.