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

Abstract

Mesoscale 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 (V g = 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 V g 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 V g = 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 V g along the East Antarctica coast induced katabatic-like surface winds throughout the day, as is commonly observed, despite the midday solar heating.

Water vapor mixing ratios and air temperatures for three martian years from Curiosity

“…Sharp, because downslope katabatic winds have piled adiabatically heated warmer air to the crater base during the night. (This warming effect has been described for Mars in Spiga et al (2009) and Rafkin et al (2016), and for Antarctican slopes in Savijärvi (2011)). The 0600LT near-surface mixing ratios do increase slowly uphill in the Steele et al simulation, but only very modestly along the 10 km distance from the MSL landing site to the sol 1880 site.…”

High‐resolution simulations of the night‐time stable boundary layer over snow

“…This scheme has operated fairly well in various conditions, e.g. in Antarctica and in the strongly stable nocturnal boundary layer of Mars (Savijärvi, 2011, 2012).…”

Interaction of katabatic winds and near-surface temperatures in the Antarctic

“…With negligible conductive heat flux through the sea ice and snow, the results also well represent conditions on a flat ice shelf below the slope. In the case of coastal polynyas or leads in the sea ice zone, however, the temperature and wind conditions would have been affected [ Heinemann , 2003; Savijärvi , 2011].…”

“…In conditions of stable stratification, the following stability function is used for momentum, heat, and moisture [ Zilitinkevich et al , 2002]: where the constant 0.003 represents the background turbulence in very stable conditions, preventing K from decreasing to zero. The model has produced realistic downslope, coastal, Antarctic, and Arctic winds and temperatures [e.g., Vihma and Brümmer , 2002; Vihma et al , 2003, 2005; Savijärvi et al , 2005; Savijärvi , 2009, 2011; Gahmberg et al , 2010; these references provide details about the model and its parameterizations]. Here a 5 km grid length on 50 sigma levels is adopted, the two lowest levels being at 1.7 m (hereinafter 2 m) and 4 m and the highest at about 6 km above the sea surface.…”