Eurasian Snow Anomaly Amplifying the Effect of North Atlantic SST on Interannual Occurrences of Spring Frosts Over Northeast China

Abstract

The spring frost over northeast China significantly affects local socioeconomic development; however, the variations and underlying mechanisms remain unclear. The present study explored the spatiotemporal attributes of spring frost days (FD) over northeast China in recent decades, and the potential mechanisms underlying their interannual variations. The results indicated an evident decline in spring FD over northeast China, accompanied by substantial interannual variation. Further analyses suggested that anomalous springtime North Atlantic tripole sea surface temperature (SST) and Eurasian snow depth are critical factors controlling the interannual variations of spring FD in northeast China. Rossby wave trains can be stimulated by the anomalous North Atlantic tripole SST (NAT), which propagates eastward through the Eurasian continent to northeast China, significantly affecting the atmospheric circulation along the pathways. This results in anomalous negative geopotential heights and cyclonic circulation over northeast China, causing low-temperature anomalies by moderating wind-induced alterations in surface heat fluxes and cloud-induced modifications in surface radiation. Meanwhile, Eurasian snow depth anomalies represent a consistent effect with NAT. The anomalous Eurasian snow depth may modify the atmosphere thickness by regulating surface heat flux, promoting the propagation of wave trains as a snow-atmosphere bridge, which enhances the impact of NAT on FD. In addition, it also triggers the Rossby wave trains to spread from high-latitude Siberia to northeast China. Both of these processes have a considerable impact on the local atmospheric circulation. Consequently, these two factors contribute to local surface cooling, thereby increasing the spring frost occurrence over northeast China.