台湾岛附近海洋对0908号台风“莫拉克”的响应特征

在模拟2009年登陆我国东部沿海的台风"莫拉克"的基础上,利用AVHRR/AMSR和SODA再分析数据和模拟结果,初步评估了GRAPES-ECOM海-气耦合模式(上海台风研究所基于GRAPES-TCM区域台风模式和ECOM海洋模式开发而成)模拟台风期间海洋响应的能力,并分析了台风期间台湾岛周围海域的海温、上升流、中尺度冷涡等的变化特点。分析结果表明,GRAPES-ECOM耦合模式较好地模拟了表层海温对台风的响应,与深水海洋响应比较,揭示了近海对台风响应的一些新特征:(1)在台湾以东海域,台风活动改变了黑潮海域海水的垂直运动,诱导黑潮南部沿岸上升流,而北部先于台风存在的上升流减弱,导致不同水深海温的最大降温位置都出现在路径左侧,与深海偏向路径右侧不同;(2)位于台湾岛东北面的彭佳屿冷涡因其形成与大陆架和黑潮有关,当台风在台湾以东洋面活动时,冷涡位于台风右前方,黑潮表层海水辐合流向大陆架,冷涡中心温度上升,强度减弱,当台风转折北上,冷涡位于台风东南侧,表层海水辐散,加强底层冷水上涌,从而增强了该冷涡的强度;(3)台风不仅加深了台湾海峡的混合层深度,还使得海水的垂直热力结构改变,并使整层海温趋于一致。

The ocean response to Typhoon Morakot (2009) in the western North Pacific boundary region

When tropical cyclones move over the shallow waters near islands and continents, the influences of the continental shelf and complicated thermodynamic conditions make typhoon forecasts much difficult. For this reason, a coupled model that consists of the hurricane GRAPES-TCM model and the ECOM ocean model has been developed in Shanghai Typhoon Institute of China Meteorological Administration. In order to evaluate the coupled model and understand the response of the western ocean boundary to tropical cyclones, numerical simulations of the landfalling process of Typhoon Morakot (2009) are conducted and compared with the satellite observations, with a focus on sea temperatures, upwelling and ocean currents. The coupled model can reasonably well simulate the dynamic and thermodynamic ocean responses during the landfall process of Typhoon Morakot. In the coastal waters, maximum sea temperature cooling occurred on the left-hand side of the typhoon track during its landfall, mainly due to the strong upwelling along the southeastern coast of Taiwan Island. Then the cold eddy in the Pengjiayu sea area to the northest of Taiwan Island weakened as the typhoon was over the Northwest Pacific and strengthened as the typhoon crossed the Taiwan Strait. The crossing of Morakot increased the mixed layer depth, leading to disappearance of the stratification of sea water in the Taiwan Strait.