Definition of the South China Sea summer monsoon onset

We analyze statistically different definitions of the South China Sea summer monsoon (SCSSM) onset are to establish a SCSSM onset time series that is more recognizable by a majority of indicators With the acknowledged index, we determine a key area (105 degrees E-112 5 degrees E, 7 5 degrees N-12 5 degrees N) and define the zonal wind component in this key area as a new SCSSM onset index, using daily mean reanalysis data of the National Center for Environmental Prediction/National Center for Atmospheric Research The atmospheric circulations before and after the onset of the SCSSM determined using the index defined in dab paper are preliminarily studied Results show that the Somalia cross-equatorial flow is enhanced, the strongest westerly wind in the tropical Indian Ocean shifts northward, the cyclone couple in the Bay of Bengal and the Southern Hemisphere weaken and move eastward, convection over the South China Sea Increases, and the subtropical high retreats from the South China Sea after the outbreak of the SCSSM By analyzing the atmospheric circulation, it is found that in 1984 and 1999, the SCSSM broke out in pentad, 29 and 23, respectively, which is consistent with the onset tames determined using our index