Twentieth century simulation of the southern hemisphere climate in coupled models. Part II: sea ice conditions and variability |
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| Authors: | Marika M Holland Marilyn N Raphael |
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| Institution: | (1) National Center for Atmospheric Research, PO Box 3000, Boulder, CO 80307, USA;(2) UCLA Department of Geography, 1255 Bunche Hall, Los Angeles, CA 90095-1524, USA |
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| Abstract: | We examine the representation of the mean state and interannual variability of Antarctic sea ice in six simulations of the
twentieth century from coupled models participating in the Intergovernmental Panel on Climate Change fourth assessment report.
The simulations exhibit a largely seasonal southern hemisphere ice cover, as observed. There is a considerable scatter in
the monthly simulated climatological ice extent among different models, but no consistent bias when compared to observations.
The scatter in maximum winter ice extent among different models is correlated to the strength of the climatological zonal
winds suggesting that wind forced ice transport is responsible for much of this scatter. Observations show that the leading
mode of southern hemisphere ice variability exhibits a dipole structure with anomalies of one sign in the Atlantic sector
associated with anomalies of the opposite sign in the Pacific sector. The observed ice anomalies also exhibit eastward propagation
with the Antarctic circumpolar current, as part of the documented Antarctic circumpolar wave phenomenon. Many of the models
do simulate dipole-like behavior in sea ice anomalies as the leading mode of ice variability, but there is a large discrepancy
in the eastward propagation of these anomalies among the different models. Consistent with observations, the simulated Antarctic
dipole-like variations in the ice cover are led by sea-level pressure anomalies in the Amundsen/ Bellingshausen Sea. These
are associated, to different degrees in different models, with both the southern annular mode and the El Nino-Southern Oscillation
(ENSO). There are indications that the magnitude of the influence of ENSO on the southern hemisphere ice cover is related
to the strength of ENSO events simulated by the different models. |
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