The sea surface temperature (SST) drops rapidly when a typhoon passes over the western North Pacific, and the cold SST is known as cold wake. In general, more intense typhoons on the day of arrival cause stronger SST cooling via turbulent oceanic vertical mixing. Moreover, after intense typhoons have passed, there are cases in which the SST decreases further, and the cold conditions persist for approximately 2 weeks. In this study, we suggest possible mechanisms by which longlasting cold SST responses to typhoon forcing are related to the generation of cold?core?like ocean circulation. The atmospheric surface cyclonic circulation causes divergent anticlockwise upper ocean currents owing to the Ekman transport, which in turn induces further upwelling and strengthens the cold SST. In the European Center for Medium?Range Weather Forecasts Ocean Reanalysis System 5, cold?core?like ocean current responses were strong in 5 typhoons among the 12 intense typhoons that passed through 30°N in the western North Pacific region from 2001 to 2019. The favorable conditions for a cold?core circulation to occur can be summarized as a slow typhoon migration speed with strong intensity, well stratification of vertical ocean layers, and the absence of large?scale strong background currents.

中纬度强台风引起的长期上层海洋温度响应

中文摘要：

当台风经过北太平洋西部时，海表面温度（SST）会迅速下降，这个冷SST的响应称为冷迹。一般来说，强台风通过海洋的湍流混合在台风抵达当天产生强的SST降温。当强台风经过后，部分SST将会进一步下降，且时间持续2周左右。本研究提出台风强迫的持续时间长的SST冷却过程的机制可能与冷核型海洋环流(cold-core-like)的产生有关。大气表层气旋性环流使上层海洋基于Ekman输送产生辐散的逆时针流场，从而激发上升流加强SST冷却。利用ECMWF提供的海洋再分析数据ERA5，2001至2019年内经过北太平洋西部30°N区域的12个强台风中，有5个台风对冷核型海洋环流的响应较强。冷核型环流发生的有利条件可概况为：台风移动速度慢、强度大、海洋垂直层化状态较好以及无大尺度强背景流。