| Summary: | Foehn winds resulting from topographic modification of airflow in the lee of mountain barriers are frequently experienced in the McMurdo Dry Valleys (MDVs) of Antarctica. Strong foehn winds in the MDVs cause dramatic warming at onset and have significant effects on landscape forming processes, however, no detailed scientific investigation of foehn in the MDVs has been conducted. As a result, they are often misinterpreted as adiabatically warmed katabatic winds draining from the polar plateau. Here we present observations from surface weather stations and numerical model output from the Antarctic Mesoscale Prediction System (AMPS) during foehn events in the MDVs. Results show that foehn winds in the MDVs are caused by topographic modification of south-southwesterly airflow which is channeled into the valleys from higher levels. Modeling of a winter foehn event identifies mountain wave activity similar to that associated with mid-latitude foehn winds. These events are found to be caused by strong pressure gradients over the mountain ranges of the MDVs related to synoptic-scale cyclones positioned off the coast of Marie Byrd Land. Foehn winds in the MDVs provide an important heat source and using stream data and satellite imagery we show these winds are intimately linked to meltwater generation and snow persistence. The intra- and inter-annual frequency and intensity of foehn events in the MDVs varies in response to the position and frequency of cyclones in the Ross Sea region. Accordingly, ENSO and other known drivers of climate variability such as the Southern Annular Mode that are known to affect cyclonic activity in the Ross Sea region may transfer a signal into the MDVs via the foehn wind regime.
|
|---|