North Atlantic forcing of autumn drought in Southwest China

Abstract

Drought often lasts long and is thus closely related to slowly varying external forcing such as sea surface temperature (SST). Here, based on observed precipitation and SST data along with NCEP–DOE reanalysis data, the possible impacts of North Atlantic SST on drought formation in Southwest China are investigated. Results show that northeast–southwest-orientated dipole SST anomalies in the mid–high latitudes of the North Atlantic are closely related to autumn drought in Southwest China; the linear correlation coefficient between them reaches 0.48 during 1979–2020, significant at the 0.001 level. The dipole SST anomalies trigger southeastward-propagating Rossby waves and induce barotropic cyclonic circulation anomalies over India and the western Tibetan Plateau. This enhances the upward motion in northern India and the western Tibetan Plateau and causes a compensating downdraft, reduced precipitation, and consequent drought formation in Southwest China.摘要干旱持续时间长, 因此往往和缓慢变化的海温异常相关. 本文利用观测降水和NCEP-DOE再分析资料, 探讨了北大西洋中高纬地区东北-西南走向的偶极子海温异常对我国西南地区秋季干旱的影响. 结果显示该偶极子海温异常可激发向东南方向传播的Rossby波, 在印度北部和青藏高原西部引起正压气旋性环流和上升运动异常, 并在我国西南地区引起补偿性下沉运动, 导致降水减少, 引发干旱.