Synergistic effects of the Tibetan Plateau snow and ENSO as preceding signals on the intensity of South China Sea summer monsoon

Based on the Rutgers University Global Snow Lab snow cover, the British Meteorological Office Hadley Center sea surface temperature (SST), soil moisture of the European Centre for Medium-Range Weather Forecasts Fifth Generation Reanalysis (ERA-5), the National Centers for Environmental Prediction National Center for Atmospheric Research reanalysis, the National Oceanic and Atmospheric Administration (NOAA) Climate Prediction Center Merged analysis of Precipitation (CMAP) and the Global Precipitation Climatology Project (GPCP) precipitation, effects of the Tibetan Plateau (TP) snow and El Niño-Southern Oscillation (ENSO) as preceding signals on the South China Sea (SCS) summer monsoon and precipitation are analyzed using methods of correlation analysis, composite analysis and regression analysis. Results indicate that the SCS summer monsoon is associated with both the TP snow and ENSO on the interannual scale. When the TP snow is higher in the west and lower in the east in spring, the tropospheric temperature in the west of the TP is abnormally low in the subsequent summer, which generates downdrafts over the plateau that flow outward. Accordingly, there are also descending airflows over the South China Sea in the lower and middle troposphere. In addition, anomalously high SSTs in the east-central equatorial Pacific may cause positive SST and tropospheric temperature anomalies in the Indian Ocean with northeasterly wind anomalies over the Northwest Pacific Ocean, which further strengthens the anticyclonic circulation anomaly over the South China Sea. When the TP snow and ENSO are synergistic, their influences on the SCS summer monsoon are stronger. Their joint effect further strengthens the lower-tropospheric anticyclonic anomaly over the South China Sea in summer, weakens the SCS summer monsoon and decreases precipitation in the South China Sea.