Unraveling the Warm Arctic？Cold Eurasia Pattern: Interplay of Arctic Amplification and Internal Variability in Shaping Midlatitude Weather

Abstract

The warm Arctic？cold Eurasia (WACE) pattern, identified as Arctic warming and midlatitude cooling over recent decades, has been a subject of intense scientific debate regarding its causal relationship and implications for midlatitude weather extremes. This study investigates the primary drivers of WACE, examining the complex interplay between external forcing and internal variability. Using the empirical orthogonal function analysis on 84 years (1941？2024) of winter (DJF) temperature over the Northern Hemisphere, we identify three dominant modes of variability: Arctic amplification (AA), the Arctic Oscillation (AO), and the Barents Oscillation (BO). AA, accounting for 27% of the total variance, captures the dominant warming pattern across the Arctic region and reflects a pronounced long-term trend. In contrast, the AO and BO modes (explaining 13.8% and 9.7%, respectively) exhibit considerable internal variability with negligible long-term trends. From 1990 to 2014, the interaction between these modes largely explains the observed WACE pattern, with AA driving Arctic warming and negative AO phase contributing to Eurasian cooling. Meanwhile, the change point detection reveals a shift in Arctic climate regimes, marking a transition from a cold Arctic regime (1947？80) to a warm Arctic regime (2004？24). During the warm regime, weakened meridional potential vorticity gradients and increased East Siberian blocking frequency are observed under negative AO and BO phases. Idealized model experiments corroborate showing that Arctic warming amplifies potential vorticity gradient reductions under negative AO and BO phases. These findings highlight the WACE pattern as driven by the intricate interaction between AA and internal variability, emphasizing the balance between external forcing and internal processes in shaping Arctic climate and midlatitude impacts.