The Atmospheric Response to Realistic Arctic Sea Ice Anomalies in an AGCM during Winter

Abstract

The influence of realistic Arctic sea ice anomalies on the atmosphere during winter is investigated with version 3.6 of the Community Climate Model (CCM3.6). Model experiments are performed for the winters with the most (1982/83) and least (1995/96) Arctic ice coverage during 1979?99, when ice concentration estimates were available from satellites. The experiments consist of 50-member ensembles: using large ensembles proved critical to distinguish the signal from noise. The local response to ice anomalies over the subpolar seas of both the Atlantic and Pacific is robust and generally shallow with large upward surface heat fluxes (>100 W m?2), near-surface warming, enhanced precipitation, and below-normal sea level pressure where sea ice receded, and the reverse where the ice expanded. The large-scale response to reduced (enhanced) ice extent to the east (west) of Greenland during 1982/83 resembles the negative phase of the Arctic Oscillation/North Atlantic Oscillation (AO/NAO) with a ridge over the poles and a trough at midlatitudes. The large-scale response was distinctly different in the Pacific, where ice extent anomalies in the Sea of Okhotsk generate a wave train that extends downstream over North America but the wave train response is greatly diminished when the model is driven by ice concentration rather than ice extent anomalies. Comparing the AGCM response to observations suggests that the feedback of the ice upon the atmospheric circulation is positive (negative) in the Pacific (Atlantic) sector. The magnitude of the wintertime response to ice extent anomalies is modest, on the order of 20 m at 500 mb. However, the 500-mb height anomalies roughly double in strength over much of the Arctic when forced by ice concetration anomalies. Furthermore, the NAO-like response increases linearly with the aerial extent of the Atlantic ice anomalies and thus could be quite large if the ice edge retreats as a result of global warming.