Influence of the Summer North Pacific Victoria Mode on Autumn Rainfall over the Greater Mekong Subregion

Abstract

This study investigates the influence of the summer Victoria Mode (VM) in the North Pacific on autumn precipitation over the Greater Mekong Subregion (GMS) between 1980 and 2010. The results show a statistically significant negative correlation between the summer VM (June–August: JJA) and autumn rainfall (August–October: ASO) in the GMS, which is independent of the effects of the El Niño-Southern Oscillation (ENSO) from the preceding winter. The positive phase of the summer VM leads to reduced autumn rainfall in key areas such as Yunnan Province, southern Myanmar, western and central Thailand, and central and southern Cambodia. Here we explored the dynamic mechanisms that link the summer VM to GMS rainfall, and identified three primary pathways: (1) the modulation of sea surface temperature (SST) anomalies and the development of a cyclonic circulation over the South China Sea, which reduces moisture transport to the GMS; (2) induced low-level divergence over the GMS, which suppresses ascending air motion; and (3) the propagation of a Rossby wave train that influences geopotential height anomalies and upper-level convergence around the GMS. These findings enhance our understanding of extratropical influences on autumn precipitation in the GMS and suggest that the summer VM could serve as a valuable predictor for seasonal rainfall forecasts, thereby assisting disaster prevention and mitigation efforts.