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. Herein observations from surface weather stations and numerical model output from the Antarctic Mesoscale Prediction System (AMPS) during foehn events in the MDVs are presented. 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 midlatitude 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. Analysis of meteorological records for 2006 and 2007 finds an increase of 10% in the frequency of foehn events in 2007 compared to 2006, which corresponds to stronger pressure gradients in the Ross Sea region. It is postulated that the intra-and interannual frequency and intensity of foehn events in the MDVs may therefore vary in response to the position and frequency of cyclones in the Ross Sea region.

Warm, dry and gusty foehn winds are frequently experienced in the McMurdo Dry Valleys (MDVs), Antarctica; however, their significance in the region's climate is unknown. Foehn events in the MDVs are caused by topographic modification of southwesterly airflow which is related to the occurrence of synoptic‐scale cyclones in the Amundsen/Ross Sea region. The intra‐ and interannual frequency and intensity of foehn events therefore varies in response to the position and frequency of cyclones in this region that are believed to be strongly influenced by the El Niño Southern Oscillation (ENSO) and the Southern Annular Mode (SAM). Here, we present a 20‐year climatology of foehn winds from observational records in the MDVs. The SAM is found to significantly influence foehn wind frequency during the Antarctic summer and autumn months, whereas ENSO only holds significant correlations with winter air temperatures in the MDVs. The positive relationship between the SAM and the foehn wind regime in summer is particularly significant as foehn winds frequently cause summer temperatures to rise above 0 °C leading to extensive melt and thaw in MDVs. Foehn winds are a major climatological feature of the MDVs with their frequency and duration affecting the region's temperature records and their trends. Accordingly, analysis of the region's weather and climate records and predictions of future impacts of climate change on the MDVs is incomplete without consideration of foehn winds and their influence. Copyright © 2012 Royal Meteorological Society

Precipitation falling in the Snowy Mountains region of southeastern Australia provides fuel for hydroelectric power generation and environmental flows along major river systems, as well as critical water resources for agricultural irrigation. A synoptic climatology of daily precipitation that triggers a quantifiable increase in streamflow in the headwater catchments of the Snowy Mountains region is presented for the period 1958-2012. Here, previous synoptic-meteorological studies of the region are extended by using a longer-term, year-round precipitation and reanalysis dataset combined with a novel, automated synoptic-classification technique. A three-dimensional representation of synoptic circulation is developed by effectively combining meteorological variables through the depth of the troposphere. Eleven distinct synoptic types are identified, describing key circulation features and moisture pathways that deliver precipitation to the Snowy Mountains. Synoptic types with the highest precipitation totals are commonly associated with moisture pathways originating from the northeast and northwest of Australia. These systems generate the greatest precipitation totals across the westerly and high-elevation areas of the Snowy Mountains, but precipitation is reduced in the eastern-elevation areas in the lee of the mountain ranges. In eastern regions, synoptic types with onshore transport of humid air from the Tasman Sea are the major source of precipitation. Strong seasonality in synoptic types is evident, with frontal and cutoff-low types dominating in winter and inland heat troughs prevailing in summer. Interaction between tropical and extratropical systems is evident in all seasons.

The hyperarid polar desert of the McMurdo Dry Valleys contains an abundance of aeolian sedimentary deposits, the largest in Antarctica, providing a unique setting for studying cold climate aeolian processes and dune morphology. Meteorological controls on sand transport and changes in dune morphology were monitored for 11 days in November-December 2004 on a barchan dune in the Victoria Valley, McMurdo Dry Valleys. Sand transport in this environment was found to be influenced by, (1) interparticle cohesion (ice-bonding);( 2) diurnal variations in the speed of thermally driven easterly valley winds due to reduced solar heating by 'night'; and (3) topographically modified foehn southwesterly winds. The threshold entrainment velocity during easterly valleys winds was 5·3 m sWarm, dry and gusty foehn southwesterly winds were found to promote aeolian processes by dislodging surface sediments, with dune morphology responding rapidly. Importantly, no diurnal signal in sand transport was observed under these conditions when wind speed and sand transport occurred independently of solar heating. Measured changes in dune morphology indicate that the dune field of the Victoria Valley under current environmental conditions is in dynamic equilibrium, with frequent up-valley sand transport by thermally generated valley winds balanced by less frequent but greater magnitude down-valley sand transport by moderate to strong foehn southwesterlies. This results in little net movement of dunes and subsequent change in the position of the dune field. Accordingly, we believe that regional-scale shifts in climate that cause change in the synoptic circulation patterns of the Ross Sea region that affect the frequency of either the up-valley easterlies or down-valley foehn winds will result in a net change in the morphology of the Victoria Valley's dune field. Such change in circulation may become apparent early as change in the morphology of the Victoria Valley sand dunes. We therefore suggest this site should be monitored as an indicator site for identifying change in regional weather and climate.

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