Subseasonal variability and the "Arctic warming-Eurasia cooling" trend.

The "Arctic warming-Eurasia cooling" trend has significantly affected the changes of weather patterns and climate extremes at lower latitudes and has attached huge attentions. However, this winter trend weakened from 2012 to 2021. In the same time period, subseasonal reversals between the warm Arctic-cold Eurasia (WACE) and cold Arctic-warm Eurasia (CAWE) patterns became more frequent and the subseasonal intensity of the WACE/CAWE pattern was still comparable with that from 1996 to 2011. This study highlighted the co-occurrence of this subseasonal variability and trend changes in the WACE/CAWE pattern based on long-term reanalysis datasets and Coupled Model Intercomparison Project Phase 6 simulations. The preceding sea surface temperature anomalies in the tropical Atlantic and Indian oceans had significant primary impacts on the WACE/CAWE pattern in early and late winter, respectively, which were confirmed by numerical experiments based on the Community Atmosphere Model and Atmospheric Model Intercomparison Project. Their coordination worked to effectively modulate the subseasonal phase reversal between the WACE and CAWE patterns just like what happened in the winters of 2020 and 2021. Findings of the present study imply that subseasonal changes need to be considered in the prediction of climate extremes at mid- to low latitudes.