The Relationship between the Typhoons Affecting South China and the Pacific Decadal Oscillation

Using typhoon data from the Shanghai Typhoon Institute of the China Meteorological Administration, the Japan Meteorological Agency’s annual Pacific decadal oscillation (PDO) index, and NCEP/NCAR reanalysis data from 1951 to 2021, correlation and composite analyses were carried out to study the relationship between the variability among tropical cyclones of different magnitudes affecting South China and the PDO. The results show that there is an obvious out-of-phase relationship between the proportion of tropical cyclones reaching a typhoon-level intensity or above in South China and the PDO index. When the PDO is in a cold (warm) phase, the sea surface temperature in the eastern and central equatorial Pacific is cold (warm), similar to the eastern Pacific La Niña (El Niño) phenomenon, and the SST in the eastern and western tropical Pacific Ocean shows a negative (positive) gradient; the subtropical high in the western Pacific Ocean is weaker (stronger) than normal, with the western ridge point to the east (west), and the 500 hPa geopotential height in the South China Sea and the area east of the Philippines is weaker (stronger), which is conducive to (unfavorable to) the formation of a monsoon trough; and the westerly (easterly) winds at high altitudes and the southwesterly (northeasterly) winds at low altitudes from the South China Sea to the Philippines are abnormally strong, and a positive (negative) vorticity at low altitudes, a low (high) sea level pressure, and strong (weak) convection are shown. These conditions are favorable (unfavorable) for the intensification of typhoons affecting South China, and as a result, the number of tropical cyclones reaching the level of typhoons or above account for a greater (smaller) proportion of those affecting South China.