Regional climate variability driven by foehn winds in the McMurdo Dry Valleys, Antarctica

Abstract

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

Föhn winds on South Georgia and their impact on regional climate

“…A number of different studies have also adopted the same arbitrary thresholds. Speirs et al (2010), Speirs et al (2013), andSteinhoff et al (2014) all identified a föhn wind by an increase of wind speed >5ms -1 , a warming of at least 1 o C and concurrent decrease in relative humidity by 5% per hour. A föhn day was defined as a day that has detected föhn onset and experiences 6 or more continuous hours of föhn conditions with wind speeds >5ms -1 from a consistent wind direction.…”

“…As a result, arbitrary limits are often set to ensure that the daily temperature rises observed are the result of adiabatic warming, instead of diabatic warming with height and/or variable winds (Gaffin, 2007). These thresholds also reduce misclassification and remove weak and brief periods that may not be of interest (Speirs et al 2013). …”

“…Gaffin, 2007) and Antarctic föhn (e.g. Speirs et al, 2013), among many others (e.g. Conrad, 1936;Osmond, 1941;Obenland, 1956;Inaba et al, 2002).…”

“…This method is analogous to the system used to identify the occurrence of föhn from AWS observations in Chapter 3. Variations of this method have been applied all over the world (see Conrad, 1936;Osmand, 1941;Obenland, 1956;Inaba et al, 2002;Speirs et al, 2013;and many others). This method is based on the assumption that the air has been warmed either by descent from heights upstream above the mountain range or by release of latent heat and fallout of precipitation on the windward slopes, leading to a warm and dry air mass descending the lee slopes.…”

“…A technique for föhn identification using surface AWS observations, which has been used extensively across many other geographical regions (see Conrad, 1936;Osmond, 1941;Obenland, 1956;Inaba et al, 2002;Speirs et al, 2013; and many others), was used to identify föhn events which occurred at King (exceeding 40ms -1 ) and relative humidities (lower than 10%). There is negligible seasonal variation in the frequency of föhn days at King Edward Point, but there is evidence of a seasonal cycle in the intensity of föhn events.…”