The Impact of Arctic Sea Ice Variability on the Atmosphere

There is a growing body of observational evidence that the climate in many parts of the Arctic is displaying statistically significant trends. The annual sea level as measured by the International Arctic Buoy Program is 3-4 mb lower during the period 1987-1994 than during 1979-1986 over the central Arctic. Arctic surface air temperatures (SAT) have warmed throughout the year, with the largest trends occurring during spring with values ranging from 0.5-2.5*C/decade. Warming during both winter and spring has resulted in a longer melting season in the eastern Arctic. Additionally, Arctic sea ice is also thinning and decreasing in extent over much, but not all of the Arctic. Observational studies indicate that there have been significant trends in the Arctic’s climate, including changes in the extent, fraction and thickness of sea ice. While there is general agreement that these changes in sea ice conditions are a result of changes in atmospheric forcing, it is not clear at present what if any effect is felt by the atmosphere to these changes in the surface ice conditions.

Given the complicated nature of ocean-ice-atmosphere interactions and the difficulty in simulating Arctic Climate using coupled models, we have focussed on how changes in sea ice influence the atmosphere by performing a number of AGCM simulations. In this research, we employ the NCAR Climate System Model (CSM) 2.0 to examine the impact on the atmosphere of the observed trends in sea ice extent, fraction and thickness. The overarching question addressed by our study is: to what extent does sea ice variability influence the atmospheric circulation?

We will present results from two sets of ensemble experiments, where the atmospheric model has been forced with observed ice conditions during the winters of 1983 (maximum) and 1996 (minimum). The atmospheric response to summer time maximum (1982) and minimum (1995) ice conditions will also be presented. From these experiments we examine how the winter and summer trends in sea ice impact the atmospheric temperature, SLP, etc., and discuss how well the simulated changes match observations. Although our experiments mainly address the one-way impact of ice on the atmosphere we will discuss sources of potential feedbacks in the broader climate system.