Exploring the Role of the Scandinavian Pattern in Summer Precipitation Prediction over Eurasia

Skillful seasonal prediction of Eurasian summer precipitation is crucial for water security and disaster resilience, yet remains a formidable scientific challenge. Current seasonal prediction frameworks rely on slowly varying boundary forcings and tend to underrepresent the potential lagged influence of mid- to high-latitude atmospheric internal variability. This study establishes that the boreal winter Scandinavian Pattern (SCAND), a dominant internal atmospheric mode in Northern Hemisphere mid-latitudes, provides a robust, previously underutilized precursor of summer precipitation anomalies. Through observational analyses and numerical experiments, we demonstrate that a positive winter SCAND forces a tripole sea surface temperature anomaly (SSTA) pattern in the North Atlantic via wind-evaporation-SST feedback. This SSTA pattern modulates synoptic-scale eddy activity, whose feedback onto the mean flow helps maintain the overlying atmospheric circulation anomalies that sustain the SSTA pattern. The SSTA pattern persists through winter into summer via air-sea interaction and the ocean's memory, establishing an effective climatic bridge across seasons. During summer, the persistent SSTA excites an eastward-propagating quasi-stationary wave train that modulates regional vertical velocities, moisture transport pathways, and surface energy budgets across Eurasia. Our findings reveal a physically interpretable cross-seasonal pathway linking winter midlatitude atmospheric variability to Eurasian summer precipitation and provide a physical basis for its potential seasonal predictability.