Searching for atmospheric signals in states of low Antarctic sea ice concentration

University essay from Stockholms universitet/Meteorologiska institutionen (MISU)

Abstract: The Antarctic sea ice region is relatively stable in extent from year to year and sees little long-term variability, the primary driver for its seasonal advance and retreat being the seasonal changes in advection of heat through the atmosphere. However, observations show a slight positive trend in its extent over recent decades. Recent work has built on the hypothesis that anomalous poleward moisture fluxes could be seen in concert with anomalous decreases in sea ice variability by providing evidence of this correlation in the Arctic sea ice region. In order to test this hypothesis and to investigate the atmospheric circulation patterns during states of low sea ice concentration in the Antarctic, records of de-seasonalized sea ice concentration anomalies are made for five regions of the Antarctic polar region, and composite distributions of variables of atmospheric circulation for the lowest 10th percentile of months with low mean sea ice concentration are compiled. Meridional moisture fluxes from these composites are tested against the entire population of meridional moisture fluxes using the Student's t-test with a confidence level of 95%, and the differences from the overall mean fields for atmospheric conditions during these cases are calculated. Of the five regions, the Ross Sea, Weddell Sea, and Pacific Ocean sections exhibit significant local moisture flux anomalies in the direction of the pole during months with low sea ice concentration, supporting the hypothesis that moisture transport into the polar region is important for the variability of sea ice in the Antarctic. The Bellingshausen - Amundsen Seas and Indian Ocean sectors show weak local signals of poleward moisture fluxes, indicating that there are other varying factors affecting the sea ice more heavily in these regions. Mean geopotential height anomalies during months with anomalously low sea ice concentration indicate that the Weddell Sea and Pacific Ocean regions are coupled with the positive phase of the Southern Annular Mode, while low sea ice concentration in the Indian Ocean as well as the Bellingshausen and Amundsen Seas regions show concurrence with the negative phase. With general circulation models predicting a persistence of the positive phase of the Southern Annular Mode in a warming climate, it is important to understand how the Antarctic sea ice region responds to the phase of this oscillation.

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