台风Chanchu(0601)变性过程中的强度变化及环境场分析

INTENSITY CHANGES AND ENVIRONMENTAL FIELD ANALYSIS OF EXTRATROPICAL TRANSITION FOR TYPHOON CHANCHU(0601)

利用非静力中尺度WRF模式模拟的台风Chanchu(0601)的输出资料,探讨了Chanchu减弱变性过程的强度及结构变化。分析结果表明:在台风Chanchu北移过程中,高层的暖心被破坏,强度快速减弱,眼壁对流发展高度降低,眼壁对流由对称结构演变为非对称,内核对流减弱。此减弱变性过程与惯性稳定度减小、垂直风切变增强、低层锋生等环境要素有关。惯性稳定度与台风强度变化一致,随着惯性稳定度降低,最大切向风减弱并不断外扩,Rossby变形半径增大从而潜热释放不集中难以维持台风强度,台风减弱;同时,内核区的高层暖心更易径向频散,从而高层暖心难以维持;环境的垂直风切变增强使台风的斜压性增强,台风垂直结构的倾斜度增大,对流发展高度降低;低层冷空气侵入台风中心趋于填塞,也利于台风强度减弱;台风登陆以后冷暖空气对比导致的锋生使得不稳定能量释放从而重新加强了Chanchu环流内的中低层对流活动,但较台风最强时刻而言对流强度减弱。总体减少的对流和降低的对流高度,导致潜热能释放减小,其向心输送也减少,不足以维持强暖心结构,最终使得台风减弱并变性。

In this paper,data from numerical simulations of the non-hydrostatic mesoscale model WRF on typhoon Chanchu(0601)is used to investigate the intensity and structural changes of extratropical transition.Results show that during the northward movement of the typhoon Chanchu,the warm core of the upper level is destroyed and the intensity is rapidly weakened.The development of the convection of the eye wall is reduced and gradually asymmetrical,and the convection of the core is weakened.This weakening process is related to environmental factors such as reduced inertial stability,enhanced vertical wind shear,and low-level frontogenesis.Inertial stability is consistent with the development of Chanchu.With the decrease of the typhoon intensity and inertial stability,maximum tangential wind is weakened and externally extended continuously and the Rossby deformantion radius is increased.Therefore,latent heat release is not concentrated and it is difficult to maintain the typhoon intensity.Meanwhile,the high-level warm core in the inner area tends to be radially dispersed,making it difficult to maintain high-level warm core.The vertical wind shear enhances the baroclinicity of the typhoon.Strong vertical wind shear increases the baroclinicity of the typhoon,causing it to tilt and the convection height is reduced.The inclination of the vertical structure of the typhoon increases and the convective development height decreases.The low-level cold air invades the typhoon center,which is also conducive to the weakening of the typhoon.During the influence of frontogenetic,the release of unstable energy reinforces the middle and lower convective activities in the Chanchu circulation.Reduced convection and convective height result in a decrease in latent heat release and centripetal transport reduction,which is insufficient to maintain a strong warm core structure and ultimately causes the typhoon to weaken.