西北太平洋暖池热状态对热带气旋活动的影响

THE EFFECT OF WARM POOL THERMAL STATES ON TROPICAL CYCLONE IN WEST NORTHWEST PACIFIC

研究1959-2003年西北太平洋热带气旋与暖池热状况的联系。结果发现暖池次表层海温与生成的台风个数具有显著相关,当暖池处于热状态时,台风偏少,生成热带风暴的位置偏向于靠近大陆的西北侧,且以西行路径为主,因此对我国的影响较为频繁。而暖池处于冷状态时,生成于西北太平洋东南侧的台风较为频繁,西北向移动至日本东南侧易于发生东北的转向。另外,对暖池冷暖状态年的环流合成发现,海表温度不是影响热带气旋年际数量异常的主要因子,而是由大气环流所引发的动力因素起决定作用。当暖池暖状态时,季风槽东端位置偏西北,对应于低层涡度和高层散度为正距平,引发中层垂直上升运动异常,有利于热带气旋在西北侧海域生成。此时500 hPa风场以东风距平为主,且西北太平洋南北侧分别为西风和东风垂直切变距平。而暖池处于冷状态时,东亚季风槽东扩,使得西北太平洋东南侧产生有利于气旋生成的环流背景,同时东亚大槽加强,中层西南风易引导热带气旋东北转向,西北太平洋南北侧分别为东风和西风垂直切变距平。

The influence of thermal states in the warm pool on tropical cyclones （TCs） in west North Pacific is investigated. There are fewer typhoons during warm years of the warm pool in which tropical storms tend to form in the northwest quadrant and move westward. Inversely, the number of typhoons, which tend to recurve northeastward to the southeast of Japan, increases in the southeast quadrant during cold years. Based on a composite analysis, the circulation-induced dynamic factors rather than thermal factors are identified as responsible for TCs activities. During the warm state, the monsoon trough retreats westwards, which leads to anomalous vorticity in low-level and divergence in high-level in the western part of west Pacific. Above-normal TCs activity is found in this area. Furthermore, wind anomalies in 500hPa determine the main track types. On the contrary, when the warm pool is in cold state, the atmospheric circulation is related to the formation of more TCs in the southeast quadrant. There are easterly shear in the south and westerly shear in the north of northwest Pacific, which is favorable for tropical cyclone development.