Relationship between the South China Sea summer monsoon withdrawal and September–October rainfall over southern China

Abstract

This study reveals a significant positive connection between the interannual variation in the South China Sea (SCS) summer monsoon (SCSSM) withdrawal and September–October rainfall over southern China. Specifically, pronounced positive rainfall anomalies can be found around southern China when the withdrawal of the SCSSM is later than normal. The occurrence of the significant SCSSM withdrawal-southern China rainfall relation may be attributed to both the atmospheric internal dynamics and the sea surface temperature (SST) anomalies over the tropical Pacific. In particular, SST warming over the tropical western North Pacific, which resembles the developing phase of a La Nina, could induce a significant anomalous low-level cyclone over the northern SCS via a Rossby wave-type atmospheric response. The southwesterly wind anomalies on the south flank of this anomalous cyclone favor late SCSSM withdrawal and contribute to more rainfall over southern China via the northward transport of water vapor. In addition, the enhanced quasi-biweekly oscillation and synoptic-scale variation (such as tropical cyclones) during late withdrawal years are also conducive to increased rainfall over southern China. Further analyses found notable interdecadal changes and asymmetry in the connection of the SCSSM withdrawal with southern China rainfall. The factors contributing to the nonstationary and asymmetric nature of this monsoon withdrawal-rainfall relationship are also briefly discussed.