| Abstrakt: |
This study examined the variation characteristics of the frequency of tropical cyclones landing in South China from July to September over the 73 years from 1949 to 2021. 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 73 years 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 243 tropical cyclones made landfall in South China between 1949 and 2021, 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 (7 cyclones), while the minimum was observed in 1950 (0 cyclones). 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 0.1 cyclones per decade in these 73 years. 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. [ABSTRACT FROM AUTHOR] |
