Mechanisms and Decadal Variability of the Warm-Pool Dipole Mode’s Influence on South China Spring Rainfall

The Warm Pool Dipole (WPD), a seesaw pattern of sea surface temperature anomalies (SSTAs) between the southeast Indian Ocean and the central-western Pacific, can strongly influence regional precipitation. This study explores its dynamical impact on South China spring rainfall and the decadal variability of this relationship. Observations and model simulations show that cold SSTAs in the central-western Pacific may excite a westward-propagating Rossby wave, while warm SSTAs in the southeast Indian Ocean induce low-pressure anomalies over the eastern Indian Ocean. These may both strengthen easterly anomalies over the western Pacific. The associated anticyclone further intensifies the western North Pacific subtropical high, increasing moisture transport to South China. Notably, the WPD’s influence weakened significantly after around 2000, becoming negligible compared to the period before. This shift is attributed to a diminished atmospheric response linked to the reduced intensity of the WPD itself in recent decades. This work identifies a new potential predictability source for seasonal forecasting of spring rainfall in South China.