(Table 2) Foehn characteristics of station in the McMurdo Dry Valleys, Antarctica

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.

受山地屏障背风侧气流地形改造作用形成的焚风（Foehn winds），常出现于南极洲麦克默多干谷（McMurdo Dry Valleys, MDVs）区域。麦克默多干谷内的强焚风在爆发时会引发剧烈升温，并对地貌形成过程产生显著影响；但迄今为止，学界尚未针对该区域的焚风开展过系统性详细科学研究。正因如此，这类焚风常被误判为源自极地高原的绝热下沉增温下降风（katabatic winds）。本文呈现了麦克默多干谷焚风事件期间的地面气象站观测资料，以及南极中尺度预报系统（Antarctic Mesoscale Prediction System, AMPS）的数值模式输出结果。研究结果表明，麦克默多干谷的焚风由南西南气流的地形改造作用所驱动，该气流从高空汇入干谷内部。针对一次冬季焚风事件的数值模拟显示，其伴随的山地波活动特征与中纬度焚风的山地波活动高度相似。进一步分析发现，这类焚风事件由麦克默多干谷山地范围内的强气压梯度引发，而该气压梯度与玛丽·伯德地沿岸的天气尺度气旋活动密切相关。对2006年与2007年气象记录的分析显示，2007年的焚风事件发生频率较2006年提升了10%，这一变化与罗斯海区域同期增强的气压梯度相吻合。据此推测，麦克默多干谷焚风事件的年内及年际发生频率与强度，或随罗斯海区域气旋的位置与发生频率变化而产生相应波动。