Impact of polar vortex variability on the wintertime low-level climate of East Antarctica: Results of a regional climate model

Abstract

Observations show that wintertime low level wind and temperatures in East Antarctica respond markedly to variations in the Southern Hemisphere circumpolar vortex. To explain this, we use output of a regional climate model RACMO/ANTI. A strong vortex extends far to the south and to relatively low atmospheric levels, which reduces the strength and directional constancy of the low-level easterlies. Over the ocean, the easterlies south of the circumpolar pressure trough (CPT) are significantly weakened and the westerlies north of it enhanced. Over the ice sheet, an increased katabatic forcing counteracts the weakening of the easterly near-surface winds. Together with the increased background temperature gradient, which enhances west-to-east turning of the large scale winds, the wind effects of vortex variability over the East Antarctic ice sheet are limited. Pronounced temperature effects are found on the ice sheet: under strong vortex conditions the lower troposphere over East Antarctica cools by 1-3 K through decreased meridional exchange of air. In addition, the weaker low-level easterlies reduce downward mixing of warm air, which causes additional cooling by up to 1.5 K at the surface.