孟加拉湾风暴Mala登陆期间地形敏感试验

A sensitivity experiment to the orographic effect on the Bengal storm of Mala during its landing

孟加拉湾是全球8个热带气旋易发生的地区之一。孟加拉湾风暴向偏北和偏东方向移动,会对中国青藏高原和西南地区形成重大影响,而孟加拉湾风暴的移动方向受到青藏高原和云贵高原大地形的影响很大。为了分析大地形对孟加拉湾风暴路径、结构变化和降水分布的作用和影响,文中利用WRF模式对2006年4月29—30日孟加拉湾风暴Mala的登陆过程进行数值模拟研究。试验结果表明:模拟风暴中心的路径和强度与实况虽有一定误差,但移动趋势均为东北方向,强度误差较小,表明WRF模式对本个例的模拟可以参考。通过不同地形高度敏感试验,分析风暴在登陆前后分别在全地形、半地形和零地形高度情况下的移动路径和速度、环流结构、动力结构以及在云南省产生的降水分布和强度。结果表明:风暴登陆前,大地形对风暴结构有间接影响,使高层出现倾斜。在风暴登陆过程中,地形的阻挡和摩擦作用能较明显影响风暴的移动路径和速度。风暴登陆后,地形抬升使风暴强度减弱,移动速度加快;结构由基本对称变为非对称,且斜压结构明显。地形对降水存在双重作用,一方面地形抬升使风暴产生的降水增加,另一方面地形摩擦使风暴强度减弱从而减少降水。

The Bay of Bengal is among the eight areas where tropic cyclones appear frequently. When a Bengal storm moves northward or eastward, it will affect weather over the Qinghai-Tibet Plateaun and the wesmorthern part of China, and also the large-scale topography of the Qinghai-Tibet Plateanu and the Yunnan-Guizhou Plateau will affect the moving path of the Bengal storm. To analyze the effect of the this topography on the path, the structure and the precipitation for the Bengal storm. The Bengal storm of Mala landfall process from 29 to 30 April in 2006 is simulated by the Weather Research and Forecast meso scale numerical model （WRF）. The results show that although there are certain errors between the simulated track and intensity for the storm and the observation, both the general moving tend and the intensity are properly simulated with small errors. The WRF can well simulate the track and precipitation of Main occurring in Yunnan province. The sensitivity experiment results from the respective schemes with the full height, half height and zero height effect on changes in the storm track are discussed, and the circulation, the dynamical structure and the precipitation over Yunnan are analyzed as well. The results show that be- fore the storm landfall, the topography affects the storm structure in an indirect way, with its structure in higher levels becom- ing slant. During its landfall, the topographic countercheck and friction are able to significantly affect the moving track and ve- locity of the storm. After its landfall, the topography caused the storm intensity to weaken and its moving velocity to quicken. On the other hand, its structure goes through the course from a basic symmetric storm to an asymmetric one with evident ba- roclinicity. The topographic effects on the precipitation are embodies in the two aspects, one is to make the precipitation in crease and another is to cause the storm intensity to weaken and thus the precipitation to decrease.