The McMurdo Dry Valleys (MDVs) located in the Trans-Antarctic Mountains, Antarctica cover approximately 4000 km2 and are mostly free of permanent snow and ice. Average mean annual air temperature at Lake Vida in the Victoria Valley, the northern most and largest of the three MDVs is -27.4°C, with an average summer air temperature of -4.6°C and winter air temperature minimums often below -60°C. The wind regime of the MDVs is dominated by thermally-generated valley and mountain wind circulations that develop between the relatively cold coastal glaciers and the warm snow and ice free Dry Valleys. These winds are disrupted during the passage of cyclonic systems in the Ross Sea – McMurdo Sound region by the onset of warm, dry and gusty down valley foehn southwesterly winds in the MDVs. These polar foehn events cause the largest short term temperature fluctuations known on Earth of > 40°C and can lead to air temperatures above 0°C during the darkness of winter. Consequently, the polar foehn affects all facets of surficial landscape processes in the MDVs including triggering the onset of summer snow and ice melt and stream flow, thawing of near surface permafrost and the subsequent release of fine grained sediment to aeolian entrainment and transport, rock weathering via aeolian abrasion, and the evolution of niveo-aeolian land forms (dunes). Despite being such an integral element of the unique hyper-arid polar MDV desert, the polar foehn has not been the subject of major scientific investigation and is frequently mistaken for katabatic airflow.
In this paper, we present an overview of the synoptic to local scale meteorology of the polar foehn events monitored in the Victoria Valley, Antarctica. These are compared to observations of foehn from mid-latitude alpine locations. Interannual variability in the frequency of the polar foehn is then discussed with regard to the influence of the El Niño Southern Oscillation phenomenon on synoptic scale circulation patterns in the Ross Sea – McMurdo Sound region of the Antarctic. Finally, we present a model that describes the evolution of foehn events in the Victoria Valley and the extreme temperature changes recorded at Lake Vida during winter foehn events.