Impacts of Winter Eurasian Snow Cover Anomalies on the Surface Air Temperature Variability over West Asia

Previous research has shown that land surface thermal anomalies in West Asia (WA) can impact regional and global climates, particularly affecting China through the eastward propagation of wave trains. However, the factors driving these anomalies in WA have not been extensively studied. Based on the observation data, this work focuses on examining the impacts of Eurasian winter snow cover on winter surface air temperature (SAT) variability over WA from 1978/1979 to 2017/2018 and explores the underlying physical mechanisms. The results indicate that a crucial snow anomaly area extending from the Baltic Sea to eastern Ural significantly influences the winter SAT anomaly in WA. An anomalous increase (decrease) in winter snow cover in this key area corresponds to the anomalously warmer (cooler) SAT in WA. This relationship is primarily driven by the albedo effects of snow cover, where more (less) snow cover induces cooling (warming) of the overlying air, altering upper-level geopotential height and influencing the intensity, duration, and frequency of local blocking events. Additionally, changes in the air temperature above the key area modify the meridional temperature gradient (MTG) between high and low latitudes, affecting the mean zonal flow in the midlatitude. Diagnosis of the thermodynamic energy equation for SAT reveals that the combined effects of variations in blocking events in high latitudes and mean zonal flow in midlatitudes alter the advection of climatological temperature by anomalous winds, which is caused by the anomalous increase (decrease) of snow cover in the key area. Consequently, this leads to changes in cold advection transported to WA, contributing to the occurrence of a warmer (colder) SAT over WA in winter.