The characteristics and temporal variability of föhn winds at King Edward Point, South Georgia
The characteristics and temporal variability of föhn winds at King Edward Point, South Georgia
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DOI：
10.1002/joc.6366
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发表时间：
2020-04
期刊：
影响因子：
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通讯作者：
D. Bannister;J. King
中科院分区：
文献类型：
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作者：
D. Bannister;J. King
多山的南格鲁吉亚亚南极洲岛屿位于强大的西风带，吹在南大洋周围。盛行的绕极西风与岛上海拔近3，000米的中央山脉相互作用，在岛上的下风侧产生温暖干燥的焚风，这是当地气候的一个重要特征。我们利用10年的自动气象站观测爱德华国王点（KEP），在东北部（气候顺风）海岸的南格鲁吉亚，发展的气候学的风在该地区的发生和属性。使用客观的标准来识别föhn的发作和停止，我们发现KEP在大约30%的时间内经历föhn条件。Föhn事件平均持续约30小时，与温度和风速的显着增加以及相对湿度的降低有关。平均而言，每4天观察到一次föhn事件，发生频率几乎没有季节性变化。然而，在南半球夏季观测到的焚风事件，平均而言，比其他季节发生的事件更长，更强烈（通过温度，相对湿度和风速的变化来测量）。当盛行西风带加强（减弱）的月份，在KEP观测到Föhn条件的时间比例增加（减少）。KEP的月平均温度与föhn分数呈正相关，但后者的变化只能解释月平均温度方差的16%。我们的结论是，虽然焚风在塑造南格鲁吉亚的当地气候中发挥了重要作用，其他过程可能是更重要的控制区域气候变率和变化。
The mountainous subantarctic island of South Georgia lies within the belt of strong westerly winds that blow around the Southern Ocean. Interaction of the prevailing circumpolar westerly winds with the island's central mountain chain, which rises to nearly 3,000 m, generates warm, dry föhn winds on the downwind side of the island, which are a significant feature of the local climate. We make use of 10 years of automatic weather station observations from King Edward Point (KEP), on the northeastern (climatologically downwind) coast of South Georgia, to develop a climatology of the occurrence and properties of föhn winds in this region. Using objective criteria to identify the onset and cessation of föhn, we find that KEP experiences föhn conditions for around 30% of the time. Föhn events last for about 30 hr on average and are associated with significant increases in temperature and wind speed, and decreases in relative humidity. On average, a föhn event is observed every 4 days, with little seasonal variation seen in the frequency of occurrence. However, föhn events observed during the austral summer season are, on average, both longer and more intense (as measured by changes in temperature, relative humidity, and wind speed) than those occurring in other seasons. The fraction of the time for which föhn conditions are observed at KEP increases (decreases) during months when the prevailing westerlies are strengthened (weakened). Monthly mean temperatures at KEP are positively correlated with the föhn fraction but variations in the latter only explain 16% of the variance of monthly mean temperature. We conclude that, while föhn plays an important role in shaping the local climate of South Georgia, other processes may be of greater importance in controlling regional climate variability and change.