双热带气旋相互作用的机制分析及数值研究(一)——物理机制的分析

Analysis and Numerical Study of the Interactions of Binary Tropical Cyclones Part I:Analysis of Physical Mechanism

本文对正压情况下双热带气旋的相互作用进行了机制分析.通过对两个理想涡旋间非线性涡度平流过程的分析,揭示了双涡气旋性互旋及其中心间距变化的涡度平流机制.分析表明,一个涡旋的切向风场对另一涡旋涡度场的平流相互作用可造成两者气旋性互旋;而一个涡旋的切向风场与另一涡旋涡度梯度间的相互作用所引起的次级环流可造成双涡中心间距的增大或减小(定义为排斥或吸引),由此提出了双涡相互作用的临界距离效应概念.对几类常用的理想热带气旋及合成热带气旋的分析证实,双热带气旋的相互作用存在这种临界距离效应,且临界距离平均在6—7个纬距左右.

In the paper, the mechanism of the interactions of binary tropical cyclones has been analyzed in the barotropic framework. Through analyzing the nonlinear vorticity advection between two idealized cyclonic vortices , the dynamical mechanism of both the mutual cyclonic rotation and the change of separation distance between two vortices have been revealed . The analytical results show that the advection of one vorticity field by the tangential wind of the other vortex may cause the two cyclonic vortices to rotate cyclonically around each other and the interaction of the tangential wind field of one vortex with the vorticity gradient field of the other vortex may increase or decrease (defined as repelling or attraction ) the separation distance . As a result, the concept of effects of the critical separation distance (or CSD) of the interactions of vortex pair is proposed . Only when the separation distance (SD) is smaller than CSD can two vortices attract mutually, otherwise they will repel to each other . By the analysis of several commonly - used idealized model tropical cyclones and composite tropical cyclone , it is found that the CSD effects may exist in the interactions of binary tropical cyclones and that on the average the CSD is about 6 - 7° latitudes which is in agreement with the synoptical fact that only when the SD is smaller than 6-7° latitudes does the binary tropical cyclone obviously attract to each other .