Changes in the Relationship Between the Variation in Spring Eurasian Snow and the Surface Temperature Over the Northern Hemisphere Around the Late 1980s

The spring snow cover extent (SCE) over central-eastern Eurasia (SCE_CEE) shows an obvious decrease around 1988. The period 1979-2019 is thus divided into two subperiods spanning 1967-1988 (P1) and 1989-2019 (P2) to investigate the interdecadal changes in the characteristics of the SCE_CEE and its relationship with surface air temperature (SAT) in the Northern Hemisphere. Positive SCE_CEE anomalies are related to a cooler Eurasia-warmer North America (CEWN) spring SAT pattern, which obviously intensifies from P1 to P2. The possible mechanisms responsible for the interdecadal changes in this snow-SAT relationship are investigated. A local energy budget analysis shows that the impact of the SCE_CEE on the overlying atmosphere is weak and the atmospheric circulation anomalies associated with the SCE_CEE variation are confined mainly to eastern Eurasia and the North Pacific in P1. In contrast, positive SCE_CEE anomalies have a significant cooling effect on the atmospheric column through anomalous heat fluxes and wind-related cold advection in P2. In P2, more SCE_CEE is associated with an anomalous cyclone in the upper atmosphere, which imposes a significant vorticity perturbation near the East Asian westerly jet core and induces eastward propagation of perturbations. The sea surface temperature anomalies in the North Pacific and the North Atlantic as well as the mean flow over the Eurasian continent help to maintain the zonal propagation of this perturbation, thus forming a hemispheric atmospheric wave pattern that contributes to the enhanced snow-CEWN SAT relationship in P2.

Automated summary

This study analyzed the interdecadal changes in the relationship between spring snow cover extent (SCE_CEE) over central-eastern Eurasia and surface air temperature (SAT) in the Northern Hemisphere. The results showed that positive anomalies in SCE_CEE are associated with a cooler Eurasia-warmer North America (CEWN) spring SAT pattern, which intensified from the first to the second subperiod.Various mechanisms, including energy budget analysis and atmospheric circulation anomalies, were investigated to understand the changes in this relationship. Positive SCE_CEE anomalies in the second subperiod had a significant cooling effect on the atmospheric column, leading to the formation of a hemispheric atmospheric wave pattern that contributed to the enhanced snow-CEWN SAT relationship.