Quantification of the Arctic Sea Ice-Driven Atmospheric Circulation Variability in Coordinated Large Ensemble Simulations.

A coordinated set of large ensemble atmosphere-only simulations is used to investigate the impacts of observed Arctic sea ice-driven variability (SIDV) on the atmospheric circulation during 1979-2014. The experimental protocol permits separating Arctic SIDV from internal variability and variability driven by other forcings including sea surface temperature and greenhouse gases. The geographic pattern of SIDV is consistent across seven participating models, but its magnitude strongly depends on ensemble size. Based on 130 members, winter SIDV is similar to 0.18 hPa(2) for Arctic-averaged sea level pressure (similar to 1.5% of the total variance), and similar to 0.35 K-2 for surface air temperature (similar to 21%) at interannual and longer timescales. The results suggest that more than 100 (40) members are needed to separate Arctic SIDV from other components for dynamical (thermodynamical) variables, and insufficient ensemble size always leads to overestimation of SIDV. Nevertheless, SIDV is 0.75-1.5 times as large as the variability driven by other forcings over northern Eurasia and Arctic.