台风“海棠”的螺旋雨带结构及特征

利用中尺度数值模式WRF对2005年7月19—20日台风＂海棠＂登陆前后螺旋雨带的结构及特征进行了模拟和诊断分析。结果表明,本次台风造成的沿海暴雨与主次两条雨带活动有关。主雨带是涡旋Rossby波激发的螺旋雨带,与850 hPa正涡度带有很好的对应关系,降水强度大,辐合层次低,处在温度和切向风速梯度最大处。次雨带辐合层次相对较高,最大温度梯度和相当位温梯度发生在700 hPa以上,无明显切向风梯度配合,其发展主要与台风中心附近的阶梯状相当位温锋区有关。当台风中雨带合并时,易造成降水增幅。台风登陆前后存在螺旋雨带的断裂现象,台风中心西侧及西北侧的中低层的辐散流场使高层的气旋性流场出现和加强,台风在高层的气旋性环流与西部低压结合,使台风西部产生辐合,引起螺旋雨带的断裂,当高层的低压形成明显的气旋式切变时,也可使切变下方螺旋雨带断裂。

Structural and Characteristic Analyses of Spiral Rain Bands around the Landing of Typhoon Haitang

In this paper, the numerical simulation and the diagnostic ananlysis of the structure and characteristic of spiral rain bands around the typhoon ＂Haitang＂ during the period of 19th to 20th July 2005 is carried out by using the WRF meso-scale model. The results are as follows. The coastal rain caused by this typhoon corresponds with the activity of the principal and secondary rain bands. The principal band caused by vortex Rossby waves is related well to the 850 hPa positive vorticity band and has heavy rainfall. Its low level convergence lies in somewhere of the maximum gradient of temperature and azimuthal winds, however the convergence level of the secondary band is higher than the former. Its maximum gradients of temperature and equivalent potential temperature θe occur above 700 hPa level without the coordination of the distinct gradient of azimuthal winds. It mainly corresponds with the ladder-shape frontal zone of θe near the center of the typhoon. The mergence of the two rain bands brings the strengthening of rainfall. During the period of the landing of Haitang, there exists the break of spiral rain bands. The divergence fields in the middle-low levels west and northwest of the typhoon center result in the strengthening of cyclonic streamline at higher levels. The cyclonic streamline at the high levels and the cyclonic flow of the low-pressure to the west of the typhoon merge into one, producing the mass convergence in this area, which splits the spiral rain bands. When the low pressure at higher levels produces the obvious cyclonic shear, which may also breaks down the spiral rain bands in the downstream.