A Stratospheric Link Between Barents-Kara Sea-Ice and the Circulation in the North Atlantic Sector

The rapid decline of ice cover in the Arctic has instilled great interest in the atmospheric community. Recent results suggest that sea ice loss in the Barents and Kara (B-K) seas in autumn and early winter cause a weakening of the stratospheric polar vortex in the subsequent months. This weakening is one of the key aspects of the well known Arctic Amplification, i.e. the faster warming of the Arctic compared to the rest of the world, and it can potentially extend the link to other regions in the troposphere. We have investigated the tropospheric response to sea ice reduction with the simplified, primitive-equations Atmospheric General Circulation Model of the Abdus Salam International Centre for Theoretical Physics. Winters have been simulated from an ensemble of initial conditions both with climatological and reduced sea-ice cover in the B-K seas. Results indicate that anomalous heat fluxes associated with early-winter reduced sea-ice cover can induce a weakening of the stratospheric circulation consistent with tropospheric forcing. This can also influence upstream changes on the lower stratosphere and troposphere, with shifts in the jet stream also influencing the Euro-Atlantic circulation. The numerical simulations provide the quantitative description of the dynamical response to surface heating associated to sea-ice reduction. The simulations will be discussed and explained using a 4-step theoretical model of the interaction between the B-K sea-ice and changes in the local tropospheric circulation, its impact on the stratosphere, and the consequent upstream influence on the Euro-Atlantic tropospheric circulation.