Impact of the Summer Tropical Atlantic Sea Temperature on the First Rainy Season Precipitation in South China

The impact of summer tropical Atlantic sea temperature (TAST) on the first rainy season precipitation in South China (FRSP) is investigated using monthly precipitation data from 160 stations in China, Hadley Center sea surface temperature (SST) data, National Oceanic and Atmospheric Administration (NOAA) outgoing longwave radiation (OLR) data, and NCEP/NCAR reanalysis data from 1979 to 2019. Correlation analysis and information flow theory indicate that a rise (reduction) in the previous summer TAST partially accounts for an increase (decrease) in FRSP. The SST increases in the critical zone (10°S–5°N, 35°W–10°E) may amplify the Walker circulation and produce abnormal subsidence across the Pacific, resulting in an easterly wind anomaly throughout the central and western equatorial Pacific during the summer. The ocean–atmosphere interactions aided in the formation of La Niña in the fall and winter that followed. The same forces govern the negative SST anomaly but in the opposite direction, which is favorable for the growth of El Niño. When the La Niña (El Niño) reaches its height in the Northern Hemisphere, convection heating intensifies (or is inhibited) in the western Pacific, triggering atypical cyclones (anticyclones) in the lower troposphere to its north. The anomalies persist until the first rainy season of the second year, resulting in the persistence of abnormal cyclones (anticyclones), which, on the one hand, contribute to the Western Pacific Subtropical High (WPSH) weakening and eastward retreating (strengthening its westward extension), thereby reducing (increasing) the transport of water vapor from the South. Thus, the WPSH reduces (increases) water vapor movement from the South China Sea to South China. On the other hand, in tropical regions, convective activity (suppression) is favorable to strengthening (weakening) the local Hadley circulation, resulting in the subsidence (ascent) anomaly in South China and suppressing (intensifying) convection. Additionally, the negative (positive) SST anomaly in the eastern Pacific energized a Pacific–North American-like wave train, and the SST anomalies in the North Atlantic energized the Eurasian (EU) wave train, resulting in negative (positive)– positive (negative) – negative (positive) geopotential height anomalies in the Eurasian mid-high latitudes region, which is unfavorable (favorable) for the cold air affecting South China.