Decadal Changes in Wintertime Frequency of Stratospheric Northern Annular Mode Events With Downward Propagation

Abstract The surface climate impact of stratospheric polar vortex anomalies depends on their downward propagation (DP) into the troposphere. We find pronounced decadal variability in the winter frequency of stratospheric Northern Annular Mode (SNAM) events that exhibit DP (1951–2024). The DP frequency of negative SNAM varies at a ∼11‐year cycle, while positive SNAM events vary at 22‐year and longer timescales. Distinguishing decades with prevalent DP would facilitate utilization of stratospheric signals in subseasonal predictions. Using an adjusted Constructed Analog (CA) approach, key SST drivers are pinpointed: cold North Pacific and warm eastern Tropical Atlantic SSTs for higher DP frequency of negative SNAM but cold Barents‐Kara Sea and cold southwestern tropical Pacific SSTs for positive SNAM. The DP frequency reconstructed by CA using observed SSTs in key regions matches observations closely. Furthermore, using predicted SSTs from CMIP6‐Decadal Climate Prediction Project yields useful reconstruction skills for DP frequency of positive SNAM.