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Thomas R. Parish
,
David H. Bromwich
, and
Ren-Yow Tzeng

Abstract

The Antarctic topography and attendant katabatic wind regime appear to play a key role in the climate of the high southern latitudes. During the nonsummer months, persistent and often times intense katabatic winds occur in the lowest few hundred meters of the Antarctic atmosphere. These slope flows transport significant amounts of cold air northward and thereby modify the horizontal pressure field over the high southern latitudes. Three-year seasonal cycle numerical simulations using the NCAR Community Climate Model Version 1 (CCM1) with and without representation of the Antarctic orography were performed to explore the role of the elevated terrain and drainage flows on the distribution and evolution of the horizontal pressure field. The katabatic wind regime is an important part of a clearly defined mean meridional circulation in the high southern latitudes. The position and intensity of the attendant sea level low pressure belt appears to be tied to the Antarctic orography. The seasonal movement of mass in the high southern latitudes is therefore constrained by the presence of the Antarctic ice sheet. The semiannual oscillation of pressure over Antarctica and the high southern latitudes is well depicted in the CCMI only when the Antarctic orography is included.

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Thomas R. Parish
,
Yuhang Wang
, and
David H. Bromwich

Abstract

Pronounced seasonal variations in the surface pressure field are present over the Antarctic continent. Surface pressures over the ice sheet decrease during the austral autumn period January–April and increase during the austral springtime months September–December. The largest changes are found over the highest portions of the Antarctic ice sheets where seasonal surface pressure changes of up to 20 hPa are common. The outstanding feature of these surface pressure changes is that typically the isallobaric contours closely follow the Antarctic orography during both transition periods, suggesting a strong seasonal diabatic adjustment within the lower troposphere. During austral autumn, the pronounced cooling of the lower atmosphere adjacent to the ice sheets leads to an enhancement of the Antarctic katabatic wind regime and hence the lower branch of the mean meridional circulation over the high southern latitudes. The mass transport provided by these drainage flows is proposed as the mechanism behind the autumn pressure falls. Numerical simulations of the evolution of the Antarctic katabatic wind regime indicate that the radiative cooling of the sloping ice fields and attendant mass transport result in a modification of the temperature and pressure fields in the lower troposphere similar to what is seen during the early austral autumn period.

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