“莫拉克”台风螺旋雨带与水平涡度的关系

Relationship of spiral rain bands and horizontal vorticity in typhoon Morakot

利用实况资料和WRF模拟资料,分析2009年8月6—10日"莫拉克"台风在台湾地区造成强降水过程中台风螺旋雨带与水平涡度的关系。结果表明:模式较好地模拟出了本次台风暴雨的发生发展过程。在7日00时—9日00时,台风外围有两条螺旋雨带,一支位于台湾的中部偏南,一支位于台湾的南部,暴雨主要位于这两支螺旋雨带上;暴雨出现在环流上升支附近,在中低层,雨带对应着较大的指向东的水平涡度,且随着水平涡度大值区移动而移动,显示出两者较密切的联系;水平涡度的大值区与垂直涡度的大值区也有较好的对应关系,存在水平涡度向垂直涡度的转化;水平涡度的旋度正值区对应上升运动区,其旋度的大值区对应强的螺旋雨带与降水。当水平涡度减小时,若水平涡度的旋度正值区存在,雨带仍然可以维持。

In this study we examine the role of typhoon spiral rain bands and the horizontal vorticity in a rainstorm case （typhoon Morakot, which occurred in Taiwan in 2009） ,using real-time observations and the Weather Research and Forecasting （WRF） model.The time period of our simulation is from 12：00 on August 6 to 00：00 on August 10, when there is typically heavy rainfall in Taiwan.Our results show that the maximum precipitation occurred on August 7 to 9, while at the same time the rainstorm in Taiwan was related to two spiral rain bands, the major spi- ral rain band of which was located in central Taiwan,while the other was located in southern Taiwan.At the low level,the rain bands consistent with the large values of the horizontal vorticity region pointed east, while at the top, the horizontal vorticity pointed west at the northern spiral rain bands. Rainstorms occurred near the vertical circulation, and moved with the large values of the horizontal vorticity region, showing that the two were closely linked.The large value of horizontal vorticity was related to the vertical vorticity, and the horizontal vorticity con- verted to vertical vorticity in the rainfall area.The positive curl of the horizontal vorticity corresponded with up- ward movement, as well as with the spiral rain bands and rainfall.When the horizontal vorticity reduced, the rain bands remained while the positive curl of the horizontal vorticity was present.