Sea-ice concentration in the Arctic and the North-Atlantic part of the sub-Arctic has undergone pronounced trends in recent decades. Although driven in large part by changes in atmospheric flow, which had shown pronounced trends toward the positive phase of the North-Atlantic/Arctic Oscillation (NAO/AO) until the past couple of years, the trend in sea ice exerts a significant feedback upon the atmospheric circulation. In a preliminary modeling study the PIs found that the feedback due to sea-ice trends was strong, compared to that of sea surface temperature, and negative. This feedback was very sensitive to the location of the area of forcing, the most sensitive area being immediately east of Greenland and in the Barents Sea, areas that have highly variable sea-ice concentrations. The PI will carry out a more detailed evaluation of the nature of the subseasonal (monthly) feedback, especially late winter into spring and summer, including fractional sea ice area coverage, which was not represented in her preliminary study. The working hypothesis is that the atmospheric response to the forcing is still prominently projected onto the dominant climate pattern so that the response may be decomposed to first order into an "indirect" part, representing the projection onto the dominant pattern of atmospheric variability, and a "direct" part, representing the part of the response that is more local to the area of forcing.
The PI will employ versions of the National Center for Atmospheric Research (NCAR) Community Climate System Model (CCSM). The model will be forced with a 1% increase per year in atmospheric carbon dioxide (CO2) concentration and the effects of doubled and quadrupled atmospheric CO2 concentration on sea ice concentration patterns will be examined. Do the patterns resemble the patterns of the observed trend during different periods of the observational record over the past century? Even if they superficially resemble any of the observed trends, it will be interesting to apply this pattern of forcing (obtained from the forced coupled model) to the atmospheric general circulation model (AGCM), since the response is highly sensitive to small differences in the area of forcing at key locations. The motivation of the study is the need to detangle forcing/response due to natural/anthropogenic causes.
The intellectual merit of the activity is that it seeks to understand and quantify the feedback of sea ice on the atmospheric circulation and its variability, which is poorly understood, while developing novel dynamical ideas regarding extratropical variability.
The broader impacts of the activity are that it will improve our understanding of phenomena that are of fundamental interest in the Arctic climate system, indeed the entire climate system, while educating and training a PhD student, as well as undergraduate students.
