The Influence of North Atlantic Dipole Sea Surface Temperature Anomalies on Autumn Drought Over Southwest China

Abstract

In recent decades, there has been a notable increase in the frequency and severity of drought events in Southwest China (SWC), which have significantly impacted agriculture and the social economy. Using sea surface temperature (SST) data from the Hadley Centre, daily meteorological drought composite index grid data and ERA5 reanalysis data, we investigate the characteristics of autumn drought in SWC and discuss its possible causes using empirical orthogonal function (EOF) analysis. The results indicate a distinct ‘Northeast–Southwest’ dipole pattern of autumn drought over SWC in the past decade, which we define as the ‘Chuan-Yu’-type drought. A British–Okhotsk Corridor (BOC) pattern Rossby wave train, presenting over Eurasia, is identified as the key factor influencing the ‘Chuan-Yu’-type drought in SWC during the autumn. The BOC-pattern Rossby wave train not only obstructs water vapour transport channels in SWC but also induces anomalous descending motions in the lower to middle troposphere over the region, leading to high temperatures and insufficient precipitation. Further investigation reveals that North Atlantic dipole SST anomalies trigger the BOC-pattern Rossby wave train in autumn. The results of the linear baroclinic model sensitivity simulations support the above conclusion. These findings will make valuable contributions to autumn drought prevention and mitigation in SWC.