The axisymmetric and asymmetric aspects of the secondary eyewall formation in a numerically simulated tropical cyclone under idealized conditions on an f-plane.
The axisymmetric and asymmetric aspects of the secondary eyewall formation in a numerically simulated tropical cyclone under idealized conditions on an f-plane.
复制标题
f 平面上理想条件下数值模拟热带气旋中次级眼墙形成的轴对称和不对称方面。
DOI：
10.1175/jas-d-18-0130.1
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Y.-H. Duan
中科院分区：
文献类型：
--
作者：
Wang H.;Y. Wang;J. Xu;Y.-H. Duan
分析了理想条件下数值模拟热带气旋二次眼壁形成的轴对称和不对称问题。与先前的研究结果一致，在SEF之前，TC切向风在SEF附近和外的边界层上和内部都经历了向外扩张。这种向外扩张与强外雨带自上而下的发展和向内传播密切相关，其上风向对流更深、更强，下风向对流更浅、更弱。由于外雨带的非绝热加热，对流层中下层出现了入流，使入流区绝对角动量向内旋转，切向风也因垂直平流而在对流区旋转。结果，当外部雨带增强并向内旋转时，扰动切向风和径向风也沿雨带向内和向下旋转。当接近初级眼壁外快速成丝区外缘时，边界层雨带下风扇区迅速轴对称。连续向内传播和轴对称化，其次与内部雨带合并，导致边界层切向风自旋，增强了地表焓通量和对流，最终形成模拟SEF。结果表明，模拟SEF是一个自上而下的过程，主要由非对称动力学触发。
The axisymmetric and asymmetric aspects of the secondary eyewall formation (SEF) in a numerically simulated tropical cyclone (TC) under idealized conditions were analyzed. Consistent with previous findings, prior to the SEF, the tangential wind of the TC experienced an outward expansion both above and within the boundary layer near and outside the region of the SEF later. This outward expansion was found to be closely related to the top-down development and inward propagation of a strong outer rainband, which was characterized by deeper and more intense convection upwind and shallower and weaker convection downwind. In response to diabatic heating in the outer rainband was inflow in the mid- to lower troposphere, which brought the absolute angular momentum inward and spun up tangential wind in the inflow region and also in the convective region because of vertical advection. As a result, as the outer rainband intensified and spiraled cyclonically inward, perturbation tangential and radial winds also spiraled cyclonically inward and downward along the rainband. As it approached the outer edge of the rapid filamentation zone outside the primary eyewall, the downwind sector of the rainband in the boundary layer was rapidly axisymmetrized. Continuous inward propagation and axisymmetrization and secondarily the merging with inner rainbands led to the spinup of tangential wind in the boundary layer, enhancing surface enthalpy flux and convection and eventually leading to the simulated SEF. Our results demonstrate that the simulated SEF was a top-down process and was mainly triggered by asymmetric dynamics.