Links Between Barents-Kara Sea Ice and the Extratropical Atmospheric Circulation Explained by Internal Variability and Tropical Forcing

Changes in Arctic sea ice have been proposed to affect midlatitude winter atmospheric circulation, often based on observed coincident variability. However, causality of this covariability remains unclear. Here, we address this issue using atmospheric model experiments prescribed with observed sea surface temperature variations and either constant or time-varying sea ice variability. We show that the observed relationship between late-autumn Barents-Kara sea ice and the winter North Atlantic Oscillation can be reproduced by simulated atmospheric internal variability but is not simulated as a forced response to sea ice. Observations and models suggest reduced sea ice is linked to a weaker Aleutian Low. We show that simulated Aleutian Low variability is correlated with observed sea ice variability even in simulations with fixed sea ice, implying that this relationship is not incidental. Instead, we suggest that covariability between sea ice and the Aleutian Low originates from tropical sea surface temperature and rainfall variations and their teleconnections to the extratropics.