Impact of Arctic sea-ice loss on the summer polar stratosphere

Arctic sea-ice plays an important role on the North Hemisphere climate and the global energy balance. However, anthropogenic climate change has caused a strong decline in sea-ice, leading to a higher increase in surface temperatures over the Arctic than at global scale. To analyse how sea-ice loss can affect atmospheric circulation at middle-high latitudes, a set of sensitivity experiments performed with the European Consortium Earth-system model (EC-EARTH) version 3P have been analysed, considering standard resolution (SR; T255, ~80 km) and high resolution (HR; T511, ~40 km) configurations. Both have 91 vertical levels with top at 0.01 hPa; hence, properly resolving the stratosphere. By changing the sea-ice albedo to open-ocean value, sea-ice concentration (SIC) is artificially reduced. The SIC loss is largest during summer and autumn (reaching 80%), consistent with the maximum solar radiation in the seasonal cycle, but still considerable (up to 20-30%) during spring and winter in regions around the sea-ice edge. Surface temperature shows strong positive anomalies over the Arctic in spring and autumn, and positive anomalies over the Hudson Bay in most of the seasons. Mean sea level pressure robustly decreases over the Hudson Bay, and shows a negative North Atlantic Oscillation (NAO)-like pattern in winter but is not robust. Zonal-mean temperature displays a shallow warming response related to sea-ice loss, with the exception of winter in HR that also shows a lower-stratospheric warming. A mid-stratospheric cooling is robustly found during summer in both model resolutions, probably associated with a reduction of shortwave radiation back to space. A 1-D radiative equilibrium model is employed to further diagnose the energy transfer along the atmospheric depth.