利用WRF数值模拟分析小型超强台风“桑美”

Numerical simulation of tiny super typhoon Saomai using WRF

利用中尺度数值模式WRF,结合WRF-Var三维变分系统,同化了雷达资料和常规、非常规观测资料,对2006年第8号小型超强台风"桑美"进行数值模拟试验.结合实况验证,WRF较好地模拟本次台风暴雨过程,基本反映实况台风演变过程.利用模式输出的具有高时空分辨率的模拟结果对"桑美"台风短时强暴雨进行诊断分析,表明"桑美"台风具有较好的对称性结构,涡旋结构紧密,云团内部气流强烈辐合上升,这是降水高度集中的动力因素;中尺度辐合带以及强回波带始终环绕中心眼区呈同心圆形状逆时针旋转,验证了台风螺旋云带的形成是产生台风暴雨的一个必要条件,"桑美"螺旋辐合带靠近台风中心,范围小、弧状明显;风切变所产生的低层辐合为强对流低层发生的动力之一;"桑美"引起的暴雨属于台风区内暴雨,具有相当充沛的水汽条件,并且水汽对降水的作用主要在中低层,以低层最强;各物理量场相互之间都有很好的对应,说明台风暴雨的发生和维持需要大尺度环境场、动力条件和水汽条件等的配合.

The mesoscale numerical model WRF is used to simulate the NO.8 typhoon Saomai in 2006.The radar data,conventional and unconventional observations are assimilated by WRF-Var.With the verification to the real situation,the process of the typhoon rainstorm is well simulated by WRF in this case that it could basically show the typhoon evolution.We use the simulation results which is model output with high spatial and temporal resolution to do diagnostic analysis on the short-term heavy rainstorm caused by Saomai.Results are shown as follows:The structure of Saomai is quite symmetrical and it has a very compact vortex and the airflow inside the cloud cluster goes through the strong convergence ascending movement,which are the dynamical factors of highly centralized precipitation;The mesoscale convergence zone and the strong echoes are always around the typhoon eye in concentric circles in counterclockwise rotation,verifying that the formation of typhoon spiral cloud band is one necessary condition for storm and Saomai's spiral convergence zone is close to the typhoon center and with small scale and large arc;the low level convergence induced by wind shear is one of the driving force of the strong convective low layer;Saomai has abundant vapour and the transfer of water vapour is advantageous and the storm triggered by Saomai is the storm happened inside the typhoon area,The vapor factor in the low laver plays on important role in the precipitation;There is a very good correspondence between the physical quantity,indicating the occurrence and maintenance of typhoons rainstorm need large-scale ambient field,dynamic conditions and moisture conditions of the match.