Roles of Atmospheric Variability and Arctic Sea Ice in the Asymmetric Arctic–Eurasia Temperature Connection on Subseasonal Time Scale

Abstract

Despite the severe impacts on Eurasian extreme weather, the mechanisms and causes of the “warm Arctic–cold Eurasia” (WACE) pattern and its opposite phase “cold Arctic–warm Eurasia” (CAWE) remain a subject of active debate. With a focus on subseasonal time scale, this study investigates the roles of atmospheric variability and Arctic sea ice in the variation of asymmetric WACE and CAWE patterns in the cold season. WACE (CAWE) patterns are predominantly driven by the temperature advection by anticyclonic (cyclonic) wave activity anomaly over Ural region. Low-frequency processes from both eddy vorticity and heat fluxes are important for the formation of the Ural wave activity anomaly. The subseasonal Arctic sea ice anomaly plays an additional role in maintaining the persistence of WACE and CAWE anomalies through surface heat flux exchange and alteration of Ural wave activity anomaly. Both comprehensive and idealized numerical experiments suggest that sea ice anomalies or thermal forcing act to maintain the WACE pattern by increasing the persistence of Ural anticyclonic anomaly through reducing background flow. The net effect of subseasonal thermal forcing on the WACE and CAWE anomalies is dependent on the mean state on longer time scale. We argue that the dominance of WACE over CAWE is mainly attributed to stronger roles of internal low-frequency atmospheric variability in driving the Ural anticyclonic anomaly and sea ice anomaly or thermal forcing in extending the persistence of the Ural anticyclonic anomaly through modulation on the background flow.