The 2007 sea ice minimum: Impacts on the Northern Hemisphere atmosphere in late autumn and early winter

Over the past several decades, the minimum Northern Hemisphere summer sea ice extent has decreased substantially. We present an analysis of the influence of declining Arctic sea ice cover on the atmosphere, specifically during the autumn/early winter following an extreme summer minimum event. Using ensemble simulations from the Weather Research and Forecast model (v 3.0.1), we compare the atmospheric response for the case of the extreme sea ice minimum of 2007 to the corresponding response for the more typical ice conditions of 1984, the year with median ice extent for the 1979-2008 satellite era. Increased open water enhances heat and moisture flux from the Arctic Ocean to the atmosphere during autumn. We characterize the fluxes both horizontally and vertically and determine the spatial breadth of their influence. The atmospheric response is characterized by a strong increase in 2 m temperature and decrease in sea level pressure locally and by remote responses in the atmospheric circulation throughout the troposphere characterized by a quasi-barotropic ridge/trough signal in North America. The circulation anomalies drive remote anomalies of temperature and precipitation over eastern North America and the North Atlantic. Advectively driven temperature anomalies, in turn, cause surface flux anomalies over remote regions such as the Great Lakes and the Gulf Stream. The maximum response, as measured by difference in 2 m temperatures over the polar cap from 70 degrees N, occurs between 10 September and approximately 15 November. The persistence of the signal over a 2 month period implies the potential for seasonal predictability of the stronger atmospheric response features. In addition, we determine the significance of prominent features, finding 95% significance in some remote features as far away as the North Atlantic.