The Essential Characteristic Of Recent Antarctic Sea Ice Increase And Its Impact Mechanisms

This study compares the distribution of trends on sea surface temperature (SST), near surface wind, sea level pressure (SLP) over the Southern Ocean in austral summer between 1979-2011 and 1950-1978, using a wide variety of data sets including un-interpolated gridded marine archives, land station data, reanalysis, and satellite products. We re-visited the observed 850 hPa westerly wind trends over the Southern Ocean during 1979-2011, and found the distribution of zonal wind trends exhibit strong regional and seasonal asymmetries. Based on precious studies, we propose that these asymmetries can be explained by a combination of tropical teleconnections and polar ozone depletion. To test our hypothesis, a series of transient atmospheric model experiments are presented, each forced with observed tropical SSTs and a different combination of time-dependent radiative forcing. To further explore the central role of tropical SSTs in recent Antarctic climate change, we emphasize the time-varying SSTs over the eastern tropical Pacific Ocean in a fully-coupled model by overriding the surface sensible heat flux to ocean to make the restored SST get closer to observation. here we called the Pacific Pacemaker experiment. The main results of these analysis are as fallowing:(1) Apart from the Antarctic Peninsula and adjacent regions, sea surface temperatures and surface air temperatures decreased during 1979-2011, consistent with the expansion of Antarctic sea ice. In contrast, the Southern Ocean and coastal Antarctica warmed during 1950-1978. SLP and zonal wind trends provide additional evidence for a sign reversal between the two periods, with cooling (warming) accompanied by stronger (weaker) westerlies and lower (higher) SLP at polar latitudes in the early (late) period. Such physically consistent trends across a range of independently measured parameters provide robust evidence for multi-decadal climate variability over the Southern Ocean and place the recent Antarctic sea ice trends into a broader context. (2) The model simulates a positive SAM-like pattern, to which ozone depletion and tropical SSTs both contribute, offsetting the insignificant direct contribution of non-ozone radiative forcing (including greenhouse gasses). In autumn, the ensemble-mean response consists of stronger westerlies over the Pacific Sector, explained by a Rossby wave originating from the central equatorial Pacific. (3) All Pacific Pacemaker runs show a IPO-like pattern in SST trends, which compares well with observation. Moving to the Antarctic, none of these runs can successfully capture the observed trends on Southern Ocean SST and the Antarctic sea ice. But, the majority of these runs show a cooling trend in the Pacific sector, which means the Pacific sector is the key region that connected to the tropical climate change.In brief, recent Antarctic sea ice increase is a part of its interdecadal oscillation and is strongly associated with the Southern Ocean cooling and strengthening westerly winds. Based on a series of AMIP simulations, the intensification of westerly winds can be explained by a combination of tropical teleconnections and polar ozone depletion. Even though, the tropical role has been emphasized in coupled model, but the model still can not capture the observed trends in southern ocean SST and Antarctic sea ice.