Interannual variation of summer compound hot and drought events in Xinjiang and its relationship with the North Atlantic sea surface temperature

Abstract

Abstract Xinjiang suffers compound hot and drought events under global warming. However, less attention has been paid to physical mechanisms of the variability of compound hot and drought events in this region. This article investigates the interannual variation of summer (June–July–August) compound hot and drought events in Xinjiang and its relationship with the sea surface temperature (SST) over the North Atlantic. The results show that its first Empirical Orthogonal Function (EOF) mode features a spatially homogenous pattern. This mode is closely connected with the simultaneous meridional negative–positive–negative SST anomalies over the North Atlantic. The summer North Atlantic tripole SST anomalies can trigger a remarkable wave train extending from the North Atlantic to Eurasia, consequently inducing an anomalous high-pressure system over the Iran–Pamirs Plateau, which is conducive to the increase of air temperature from the surface to the upper troposphere over Xinjiang. The warmer troposphere further strengthens the western Asian subtropical meridional temperature gradient and thereby enhances the westerly wind to the north flank of the West Asian subtropical westerly jet (WASWJ). As a result, the WASWJ is displaced northward, which intensifies the sinking motion and prevents the water vapor transport to Xinjiang, leading to a decrease of precipitation in the target region. The higher temperature and less precipitation contribute to the occurrence of compound hot and drought events over Xinjiang. Numerical simulations based on the Community Atmospheric Model version 4 (CAM4) further confirm the relationship between the North Atlantic tripole SST anomalies and compound hot and drought events in Xinjiang during summer on the interannual time scale.