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 associated circulation anomalies. 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 delineate a complete ocean-atmosphere pathway that links boreal winter circulation patterns to summer precipitation anomalies. This work not only demonstrates that mid-high-latitude internal atmospheric patterns are physically predictable signals for Eurasian precipitation but also offers a new precursor and forecasting framework for seasonal climate prediction.