Antarctic local wind dynamics and polynya effects on the Adélie Land coast

Abstract

AbstractMesoscale winds on the sloping coast of Adélie Land in East Antarctica were studied via idealized clear‐sky integrations with a two‐dimensional model. The calm‐case (Vg = 0) wintertime surface winds were steady katabatic southeasterlies. They were enhanced to a strong downslope low‐level jet (LLJ) during a southerly geostrophic flow but damped during a moderate westerly ‘counter‐katabatic’ flow. A strong westerly flow could overwhelm the katabatic component while a northerly Vg induced strong coastal easterlies with an easterly LLJ. On‐slope flow without the katabatic forcing generated a barrier effect. An ice‐free wintertime zone (a coastal polynya) increased the coastal 2 m winds by about 50% (and drag on the ice floes, by 125%) through the induced extra land breeze circulation and unstable stratification. The midsummer morning coastal winds were also katabatic in the morning as the slopes cooled rapidly after midnight. In a prevailing flow these behaved much as in wintertime but were strong only at 0400–0700 hours local time. By 0800–0900 hours local time the snowy slopes were melting in sunshine. With Vg = 0 this induced weak anabatic winds up the slope. At the coast a midday ‘sea breeze’‐like circulation was present, insensitive however to the sea state (frozen vs. open) or the coast state (snowy vs. black rock) of the model. These anabatic winds were quite weak and hence easily overwhelmed by any larger‐scale flow, surviving only during a weak westerly flow. The typically easterly Vg along the East Antarctica coast induced katabatic‐like surface winds throughout the day, as is commonly observed, despite the midday solar heating. Copyright © 2011 Royal Meteorological Society