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Abstract
Recent studies suggest that warming trends across West Antarctica and the Antarctic Peninsula and sea ice loss in the adjacent Amundsen and Bellingshausen Seas are linked to changes in the regional atmospheric circulation, represented by the Amundsen Sea low (ASL). Importantly, changes in the ASL have similarly been tied to forcing from the tropics. Here, several model simulations from the Community Atmosphere Model, version 4, are investigated in order to understand the relative roles of tropical sea surface temperature variability and radiative forcing on the variations in trends in the ASL. In comparing across the simulations, it is observed that the addition of time-varying extratropical SSTs and sea ice conditions in general have a much smaller impact on the ASL than tropical SSTs or radiative forcing. Tropical forcing alone explains much of the climatological variability and extreme intensities of the ASL (both strong and weak relative central pressures). The role of radiative forcing is best observed in the ASL trends, with this simulation leading to a marked deepening of the ASL and pressures across the Southern Hemisphere that is consistent with atmospheric reanalysis in austral summer. In austral winter, the simulation with radiative forcing produces stronger trends than observed in reanalysis data, perhaps reflecting the need to couple to an ocean–ice model in order to more realistically simulate the ASL changes. Together, the results suggest that models need to include both the effects from tropical SST variations and radiative forcing when understanding historic and future variations in the ASL.
Abstract
Recent studies suggest that warming trends across West Antarctica and the Antarctic Peninsula and sea ice loss in the adjacent Amundsen and Bellingshausen Seas are linked to changes in the regional atmospheric circulation, represented by the Amundsen Sea low (ASL). Importantly, changes in the ASL have similarly been tied to forcing from the tropics. Here, several model simulations from the Community Atmosphere Model, version 4, are investigated in order to understand the relative roles of tropical sea surface temperature variability and radiative forcing on the variations in trends in the ASL. In comparing across the simulations, it is observed that the addition of time-varying extratropical SSTs and sea ice conditions in general have a much smaller impact on the ASL than tropical SSTs or radiative forcing. Tropical forcing alone explains much of the climatological variability and extreme intensities of the ASL (both strong and weak relative central pressures). The role of radiative forcing is best observed in the ASL trends, with this simulation leading to a marked deepening of the ASL and pressures across the Southern Hemisphere that is consistent with atmospheric reanalysis in austral summer. In austral winter, the simulation with radiative forcing produces stronger trends than observed in reanalysis data, perhaps reflecting the need to couple to an ocean–ice model in order to more realistically simulate the ASL changes. Together, the results suggest that models need to include both the effects from tropical SST variations and radiative forcing when understanding historic and future variations in the ASL.
