初始外围尺度与加热对台风次眼墙形成的影响

Influence of initial outer-core size and diabatic heating on the secondary eyewall formation of tropical cyclones

台风次眼墙位于主眼墙外侧,由次对流环和低层切向风次极大值两个基本结构组成。本文通过一系列理想数值试验讨论了不同初始涡旋外围风场结构对次眼墙形成的影响作用以及关键动力学过程。结果表明,次眼墙形成的时间和位置与初始涡旋外围尺度显著相关:随着外围尺度递减,台风从形成完整双眼墙、伪双眼墙到没有双眼墙逐步过渡,次眼墙形成时间推迟且位置更加靠近台风中心。动力学分析发现,初始外围尺度可控制外雨带分布,雨带的非绝热加热主导了主眼墙外围边界层径向入流和绝对涡度径向输送的分布和大小。绝对涡度径向输送和摩擦耗散的相对大小及位置决定了次眼墙低层切向风次极大值出现的可能性和位置。动量强迫对低层切向风次极大值的大小仍有贡献。

The secondary eyewall of a tropical cyclone is located outside the primary eyewall and consists of two basic characters: a secondary convective-ring and a secondary tangential wind maximum. Based on a series of idealized numerical simulations, this paper investigates the influence of initial wind structures on the Secondary Eyewall Formation(SEF) and the key dynamic process. Results indicate that there is a significant correlation between the time and location of the SEF and the initial outer-core size. With decreasing initial outer-core sizes, simulated vortexes undergo canonical SEF, fake SEF and no SEF successively. The time of the SEF becomes later and the location of secondary eyewall becomes closer to the vortex center. Dynamical analysis shows that the initial outer-core size controls the distribution of Outer Rainbands(ORBs). Diabatic heating of ORBs dominates the distributions and intensities of boundary layer inflow and radial flux of absolute vorticity outside the primary eyewall. The relative intensities and positions of this radial flux of absolute vorticity and friction determine the possibility and location of the secondary tangential wind maximum. The momentum forcing can also contribute to the increase of secondary tangential wind maximum.