Intraseasonal changes and spatial patterns of Arctic warming influence on circulation and temperature anomalies in Eurasia.

The “Warm Arctic — Cold Eurasia” (WACE) pattern is a manifestation of Arctic amplification's influence on mid-latitude climate. Despite extensive research, crucial aspects such as its intraseasonal dynamics and the precise role of atmospheric blocking remain highly debated. This study presents a comprehensive analysis of the spatiotemporal variability of the WACE pattern and its connection to blocking anticyclones using ERA5 reanalysis data (1979–2023) on a 2.5° × 2.5° grid. We employed two independent methods to calculate the WACE index — based on temperature anomaly differences between the Barents-Kara Seas (BKS) and Central Eurasia (CE) and via Empirical Orthogonal Function (EOF) analysis, which objectively identified the WACE pattern as the second leading mode of temperature variability, explaining ~17 % of the variance. Atmospheric blocking was diagnosed using the GHGS index at the 500 hPa level, distinguishing between northern (50–70° N) and southern (40–60° N) regimes to account for the seasonal shifts in the blocking latitude. Our analysis reveals a sustained restructuring of atmospheric circulation since the early 2000s, marked by a statistically significant intensification of the WACE pattern in the autumn-winter period (a trend of 1.4 °C per decade for December-February) and a fundamental shift in its seasonal progression. It has been found that in the early cold season (October–November), the WACE pattern is most strongly correlated with the northern blocking events. The longitudinal focus of this correlation has shifted eastward, with its peak located over the Western Siberian sector (70–90° E), rather than the traditional Ural Mountains. The correlation coefficients in this sector for the northern regime reach 0.7 in October, underscoring a robust linkage. This points to a transformation of the primary mechanism behind WACE formation after the year 2000, which is now governed by high-latitude blocking over the increasingly ice-free Kara Sea. The observed systemic shift towards high-latitude, “Rex”-type dipole blocks effectively shortens the transitional autumn period, leading to an earlier and more abrupt establishment of winter-like circulation. These findings are important for understanding fundamental changes in seasonal circulation over Eurasia and for improving the predictability of extreme cold weather events.