Interdecadal Variations of the Scandinavian Pattern

This study investigates the interdecadal variation of the Scandinavian (SCA) pattern and corresponding drivers during the boreal winter. It is found that the SCA pattern experiences a prominent regime shift from its negative to positive phase in the early 2000s based on several reanalyses. This interdecadal change contributes to an extensive cooling over Siberia after the early 2000s, revealing its importance for recent variations of climate over Eurasia. The outputs from 35 coupled models within phase 6 of the Coupled Model Intercomparison Project (CMIP6) are also analyzed. The results show that the interdecadal change of the SCA is weak in response to external forcings but can be largely explained by in-ternal variability associated with a change of precipitation over the tropical Atlantic. Further analysis indicates that the enhanced tropical convection induces poleward propagation of Rossby waves and further results in an intensification of geopotential height over the Scandinavian Peninsula during the transition to positive SCA phases. These findings imply a contribution of tropical forcing to the observed interdecadal strengthening of the SCA around the early 2000s and offer an insight into the understanding of future climate change over the Eurasian continent.