利用NCEP/NCAR再分析资料和美国NOAA向外长波辐射(OLR)等资料, 对2008年登陆我国热带气旋活动具有初台登陆早、秋台集中、登陆热带气旋比例高等特点及其成因进行了初步分析。结果表明, 南半球冷高压发展引发的越赤道气流增强, 使得赤道西风加强并向东延伸, 热带辐合带对流活跃, 有利于热带气旋生成; 并且, 在中纬度地区冷空气活动不频繁、西南季风涌活跃、副高位置偏北偏西等背景条件配合下, 登陆热带气旋多而集中。运用大气视热源和全型垂直涡度倾向方程, 发现热带辐合带增强北推, 使得热带气旋接连产生, 强降水产生的非绝热加热异常, 促使副高位置发生显著北抬和西伸。当一个时期生成的热带气旋多而集中, 副高的这种异常状态就会维持, 从而造成这一时期热带气旋西行, 频繁登陆我国。

Based on the NCEP/NCAR reanalysis data and the Outgoing Longwave Radiation (OLR) data from the NOAA, the authors analyze the landfall tropical cyclones in China during 2008. The characteristics of the 2008 tropical cyclone season include the first tropical cyclone coming in much earlier, the autumn tropical cyclones appearing close together, and high proportion of landfall tropical cyclones. The results show that, with the development of the cold high in the southern hemi-sphere, the equatorial low-level jet was intensified, which strengthened the equatorial westerly wind and spread it eastward, and the convection in the Inter-Tropical Convergent Zone (ITCZ) was more active. These circu1ation conditions resulted in the formation of tropical cyclones. With infrequent cold air in the mid-latitude areas, including the developing southwest monsoon and northwestward advance of the subtropical high, the frequency of landfall tropical cyclones was greater than norma1. By applying the atmospheric heat sources and the complete form of the vertical vorticity tendency equation, it is found that with the ITCZ strengthened and spread northward, the tropical cyclones originated frequently, strong precipitation lead to the ab-normal non-uniform heating that played an important role in the northwestward advance of the subtropical high. As the tropi-cal cyclones occurred frequently for some time, the subtropical high could keep such abnormal state, which leads to the tropi-cal cyclones moving westward and landfall frequently in China.