7—9月登陆华南热带气旋频数异常与大气环流和海温的关系

利用1949—2021年中国气象局上海台风研究所热带气旋资料、NCEP/NCAR再分析资料、NOAA重构的海表温度资料（SST）和大气向外长波辐射（OLR）资料，采用线性趋势分析、Mann-Kendall检验等方法分析了近73年7—9月登陆华南热带气旋频数的变化特征。采用合成分析的方法研究7—9月登陆华南热带气旋频数异常与同期大气环流和海温的关系。结果表明，1949—2021年7—9月，登陆华南热带气旋有243个，年均3.3个，占全年登陆总数的70.2%。登陆华南热带气旋频数具有显著的年际和年代际变化特征。1973年最多（7个），1950年最少（0个）；在1990年代中期由前期偏多转为后期偏少，但没有突变发生。近73年7—9月登陆华南热带气旋频数以0.1（10a）-1的速率减少。7—9月登陆华南热带气旋频数异常与大气环流和海温异常密切相关，在异常多、少年同期：（1）大气环流差值场上，南亚高压偏强、偏东、偏北，副高偏西、偏北、偏强，110°E以东的赤道东风引导气流偏强，季风槽加强，北半球中低纬海平面气压场东高西低，北高南低，同时南海、热带西太平洋对流活动加强。（2）海温差值场上，赤道中东太平洋偏冷，西太平洋暖池偏暖，沃克环流加强。高中低层大气环流和海温这种差异可能是导致登陆华南热带气旋频数异常的原因。

Anomalous Frequency of Tropical Cyclones Landing in South China and its Relationship with Atmospheric Circulation and SST from July to September

This study examined the variation characteristics of the frequency of tropical cyclones landing in South China from July to September over the 73years from 1949 to2021.Data employed included those from the Shanghai Typhoon Institute of the China Meteorological Administration ,NCEP/NCAR reanalysis data,NOAA reconstructed sea surface temperature (SST)data,and atmospheric long-wave radiation (OLR) data.The variation characteristics of the frequency of tropical cyclones landing in South China from July to September in the past 73years were analyzed by using methods such as linear trend analysis and Mann Kendall test .The relationship between the anomalous frequency of tropical cyclones landing in South China from July to September and the atmospheric circulation and early SST was analyzed by using synthesis and correlation methods .The results showed that a total of 243tropical cyclones made landfall in South China between 1949 and2021,with 70.2% occurring from July to September (averaging 3.3 cyclones per year ).The frequency of tropical cyclones landing in South China exhibited significant interannual and interdecadal variations .The maximum frequency was found in 1973 (7cyclones ),while the minimum was observed in 1950 (0cyclones ).There was a shift from more in the early stages to less in the later stages in the mid- 1990s,although no abrupt changes were observed .The frequency of tropical cyclones landing in South China has decreased at a rate of 0.1cyclones per decade in these 73years .The anomalous frequency of tropical cyclones landing in South China from July to September was closely related to atmospheric circulation and SST anomalies .During the same period in anomalous years ,the following patterns were observed :(1)In the difference field of atmospheric circulation ,the South Asia High was stronger and shifted eastward and northward ,while the Subtropical High was stronger and shifted westward and northward .The easterly flow east of 110°E in the equatorial region intensified ,along with a strengthened monsoon trough .The sea-level pressure field in the middle and low latitudes of the Northern Hemisphere showed an east-high ,west-low pattern ,with higher pressure in the north and lower pressure in the south .At the same time ,convective activities in the South China Sea and the western Pacific in the thermal zone were strengthened .(2)In difference field the SST ,the equatorial middle and eastern Pacific was cooler ,the western Pacific warm pool was warmer ,and the Walker circulation was strengthened .The difference in atmospheric circulation and SST in the upper ,middle and lower levels may be the reason for the anomalous frequency of tropical cyclones landing in South China .