Arctic sea ice loss drives increasing Arctic wind speeds with combined impact on surface roughness and boundary layer stability

Abstract The Arctic is undergoing a pronounced and rapid transformation in response to changing greenhouse gases, including reduction in both sea ice spatial extent and sea ice thickness and projected increase in near-surface winds. Other studies have suggested that the increasing winds may be driven by changing surface roughness and/or stability, but the coupled relationship between the changing winds and changing sea ice in different regions and seasons is not yet well understood. This study disentangles ways in which changing surface conditions affect the changing winds regionally and seasonally. We analyze 50 experiments from the Community Earth System Model version 2 Large Ensemble (CESM2-LE) as well as 5 experiments using CESM2 in which sea ice roughness has been decreased to be equivalent to what it would be over the smoother, open ocean (SMOOTH). We find that with a smoother surface there is a small reduction in the surface momentum flux, leading to faster mean wind speeds and slower mean ice speeds. In SMOOTH, the reduction in surface roughness due to ice loss is negligible, resulting in weaker increasing trends in near-surface winds, particularly in Autumn and Winter. There are no significant coupled impacts of surface roughness change on the sea ice mean state or loss trend. Because both the CESM2-LE and SMOOTH experience statistically indistinguishable sea ice loss trends that impact near-surface atmospheric temperatures, the experiments have very similar changes in atmospheric stability which also influences the near-surface winds. Therefore, in CESM2-LE, the near-surface increasing wind speed trends result from both decreases in surface roughness and reduction in near-surface atmospheric stability that are the result of sea ice loss.