Interannual relationship between South Pacific meridional sea surface temperature dipole and rainfall anomalies over South China in late-spring to early-summer without ENSO impact

The first rainy season (FRS) in South China from late-spring to early-summer represents the beginning of the summer monsoon rainy season over eastern China. This study investigates the interannual relationship between the South Pacific meridional sea surface temperature (SST) dipole (SPMD) and the concurrent FRS precipitation anomalies over South China during April-June (AMJ) without El Nino/Southern Oscillation (ENSO) impact. During AMJ, after removing the concurrent ENSO signal through the linear regression, the first empirical orthogonal function (EOF) mode of SST anomalies in the South Pacific exhibits a meridional dipole with warming in the tropical southeastern Pacific and cooling in mid-latitudes of the South Pacific. The first EOF mode is referred to as the SPMD pattern. The off-equatorial enhanced diabatic heating associated with the northeastern pole of the SPMD triggers low-level cross-equatorial northerlies in the tropical north central Pacific (TNCP) through the Matsuno-Gill type response. The anomalous northerly and its associated TNCP SST cooling lead to a Northwest Pacific anomalous anticyclone (NWP-AAC) via the wind-evaporation-SST feedback. The atmospheric general circulation model sensitivity experiments further suggest that the SPMD can induce the NWP-AAC directly or collaboratively with the TNCP SST cooling. Additionally, anomalous moisture can be transported from the tropical western Pacific into South China, giving rise to enhancement of the FRS precipitation. The Liang-Kleeman information flow for causality analysis and ensemble mean of 30-member atmospheric model simulation results further suggest a robust physical pathway that the SPMD is related to the FRS precipitation over South China when ENSO absents. Our results may deepen the understanding of interannual rainfall variability in South China in non-ENSO years.