2013年“苏力”台风西行登陆引发闽南大暴雨成因的模拟研究

A Numerical Investigation of the Formation Mechanism for the Extremely Heavy-Rain Event in Southern Fujian Induced by Westward-Moving Typhoon Soulik in 2013

利用中尺度数值模式对2013年7月13~14日"苏力"台风引发福建南部大暴雨的天气过程进行了数值模拟、诊断分析和敏感性试验。结果发现:台风环流内强的正差动涡度平流和强的低层暖平流叠置是台风对流暴雨形成的有利大尺度强迫环境。台风登陆后移动旋转过程中,其风场、假相当位温场(θse)、水汽场、对流有效位能(CAPE)、对流不稳定度的空间结构及其正相对涡度、辐合区随着台风旋转在不断发生变化,台风环流内高θse和高比湿气团的影响、带有CAPE气流的输入、低层气流汇合或风速辐合、对流不稳定以及局地地形强迫等共同作用是闽南大暴雨发生的主要原因,强降水区主要位于环境风垂直切变的下游和左侧。此西移经台湾北侧的台风个例中,台湾地形可能主要通过改变台风环流内降水及其非绝热加热分布,进而影响台风的结构和移动路径,最终影响台风暴雨的强度和落区。闽南局地地形在台风大暴雨的形成中起到了一定的增幅作用,海陆摩擦差异造成的风速辐合在台风移近到登陆阶段对台风北侧偏东气流内降水具有不可忽视的增幅作用。

The extremely heavy rain event induced by the westward-moving typhoon Soulik during 13-14 July 2013 is investigated through numerical simulation, diagnostic analysis, and sensitivity experiments using a mesoscale numerical model. The results show that the superposition of strong positive differential vorticity advection and strong low-level warm advection in the typhoon circulation is the large-scale environment favorable for the formation of heavy convective rainfall. After the typhoon landed, its spatial structure of wind, pseudo equivalent potential temperature （θse）, high moisture, convective available potential energy （CAPE）, convective instability and positive vorticity, and convergence area all varied with the typhoon rotation during the period of moving and rotating. The combined effect of high θse air mass, the inflow of instable air, the low-level convergence or wind speed convergence in typhoon circulation, the convective instability and local topographical forcing was the main reason for the formation of the extremely heavy rainfall in southern Fujian Province. The heavy rainfall was mainly located in the downstream and left side of the environmental vertical wind shear. In this case, the west-moving typhoon passed north of Taiwan, where the topography might affect the moving path and structure of the typhoon through changing the typhoon rainfall distribution and associated diabatic heating, eventually affected intensity and location of the heavy rainfall. The local topography in southern Fujian Province might exert an enhancing influence on the typhoon extremely heavy rainfall. The wind speed convergence induced by differences in friction between the land and sea surface played a critical role in the rainfall within the easterly flow to the north of the typhoon during its moving-close-to-land and landing period.