Precursor of deep Arctic warming during winter: reduced moisture over the Beaufort Sea during autumn

The deep Arctic winter warming over the Barents–Kara Sea (BKS), extending into the upper troposphere, exerts important influence on the mid-latitude climate, which has been widely studied. However, the causes of deep Arctic winter warming are unclear yet. This study explored the influence of simultaneous and preceding Arctic atmospheric moisture on the deep Arctic winter warming, using both reanalysis data and model simulations. In the deep Arctic warming winters, the moisture over the BKS increases throughout the troposphere, which contributes to deep Arctic warming via absorbing more longwave radiation. The reduced moisture over the Beaufort Sea (BFTS) in the preceding autumn acts as a precursor through two dynamical pathways: (1) Inducing zonal wavenumber-1 disturbances in the stratosphere during autumn, which propagate downward into the troposphere and lead to an anomalous high over northern Eurasia in the subsequent winter. (2) Inducing a positive North Atlantic Oscillation (NAO) phase in autumn via the eastward propagation of the wave trains. The positive NAO, coupled with anomalous sea surface temperature in the North Atlantic, persists and even intensifies into the subsequent winter. The anomalous high over northern Eurasia and the positive NAO phase in winter are favorable for the increased moisture over the BKS and deep Arctic warming in winter. The model simulations further support the above results. This research is beneficial for enhancing the understanding of climate variations in the Arctic and mid-latitude regions, and providing theoretical support for climate prediction.