Are mid-latitude circulation responses linearly additive to regional Arctic temperature anomalies? Insights from an idealized Atmospheric General Circulation Model.

Previous studies have documented the impact of the Arctic sea ice loss and associated warming on the mid-latitude weather and climate, especially the influence of dramatic sea ice retreat over the Barents-Kara Sea on the North Atlantic, Europe and Siberia regions. However, less attention has been given to other geographical locations over the Arctic, and to the linear additivity of the circulation response to regional Arctic sea ice loss and Arctic temperature anomalies. Using a simplified dry dynamical core model, we demonstrate that, responses to regional Arctic temperature anomalies over the Barents-Kara Sea, Baffin Bay-David Strait-Labrador Sea and East Siberia-Chukchi Sea, separately, cause similar equatorward shift of the tropospheric jet, but different stratospheric polar vortex responses. In addition, responses to regional Arctic temperature anomalies are not linearly additive, and the residual resembles a positive Northern Annular Mode-like structure. Additional experiments further diagnose the role of the stratosphere in the non-linearity, and we show that stratosphere-troposphere coupling plays an important role.