标题： 旋转流在纬向不对称热带经向环流中主导了突然的季节变化 显示英文标题

标题： Rotational Flow Dominates Abrupt Seasonal Change in Zonally Asymmetric Tropical Meridional Circulation

摘要： 热带经向环流的季节性在不同地区演化方式不同，它控制着季风的开始和撤退以及热带降水的迁移，从而影响热带和副热带地区的农业生产力和灾害准备。 通过定义一个伪经向翻转流函数（{\Psi }pseudo）并定义一个新的矢量型、双分量指数（ASCI），我们诊断了热带经向环流的纬向不对称突然季节变化（ASC）。 {\Psi }pseudo 在任何纬度周围的一个纬向圆上平均后收敛到传统的经向翻转流函数（{\Psi }m）。 通过对水平速度场应用亥姆霍兹分解，将{\Psi }pseudo 分解为旋转分量和发散分量，我们定量比较了水平旋转流和发散流对突然季节变化的贡献。 我们发现与强深层对流相关的纬向区域表现出最显著的热带经向环流突然季节变化，所有表现出ASC的子区域都包含热惯性较低的陆地。 特别是，与纬向对称的哈德莱环流情况相比，旋转流而非热直接发散流在热带纬向不对称ASC中占主导地位，尽管发散流也对与深层对流相关的纬向区域的ASC有所贡献。 我们认为热带罗斯比型涡旋与外热带涡旋及热带环流之间的相互作用对于热带哈德莱环流的纬向不对称ASC是至关重要的。 显示英文摘要

摘要： The seasonality of the tropical meridional circulation evolves differently across different regions, governs the onset and retreat of monsoons and migration of tropical precipitation, thereby influencing agricultural productivity and disaster preparedness in the tropics and subtropics. By defining a pseudo meridional overturning streamfunction ({\Psi}pseudo) and defining a new vector-type, dual-component index (ASCI), we diagnose zonally asymmetric abrupt seasonal change (ASC) of tropical meridional circulation. {\Psi}pseudo converges to traditional, meridional overturning streamfunction ({\Psi}m) after being averaged over a zonal circle around any latitude. By applying the Helmholtz decomposition to horizontal velocity fields so as to decompose {\Psi}pseudo into rotational and divergent components, we quantitatively compare the contributions of horizontally rotational and divergent flows to the abrupt seasonal change. We find that the zonal sectors associated with strong deep convection exhibit the most pronounced ASC of tropical meridional circulation, and all of subregions exhibiting ASC contain landmass with low heat inertia. Particularly, in contrast to the case of zonally symmetric Hadley cell, rotational flow, rather than the thermal-direct divergent flow, dominates the zonally asymmetric ASC in the tropics, although the divergent flow also contributes to the ASC over the zonal sectors associated with deep convection. We suggest that the interplay between tropical Rossby-type eddies with extratropical eddies and tropical circulation is essential to the zonally asymmetric ASC of tropical Hadley circulation.