Impact of polar vortex variability on the wintertime low-level climate of east Antarctica: results of a regional climate model
Van Den Broeke, M. R.
Van Lipzig, N. P.M.
- Publisher: Co-Action Publishing
(issn: 1600-0870, eissn: 0280-6495)
Observations show that wintertime low level wind and temperatures in East Antarctica respondmarkedly to variations in the Southern Hemisphere circumpolar vortex. To explain this, we use outputof a regional climate model RACMO/ANT1. A strong vortex extends far to the south and to relativelylow 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 significantlyweakened and the westerlies north of it enhanced. Over the ice sheet, an increased katabatic forcingcounteracts the weakening of the easterly near-surface winds. Together with the increased backgroundtemperature gradient, which enhances west-to-east turning of the large scale winds, the wind effectsof vortex variability over the East Antarctic ice sheet are limited. Pronounced temperature effects arefound on the ice sheet: under strong vortex conditions the lower troposphere over East Antarcticacools by 1–3 K through decreased meridional exchange of air. In addition, the weaker low-level easterliesreduce downward mixing of warm air, which causes additional cooling by up to 1.5 K at thesurface.DOI: 10.1034/j.1600-0870.2002.201383.x