Variability In The Near-surface Winds Over The Antarctic Ice Sheet During The Last 50 Years And Their Causes

In the context of the recent continuous global warming,much attention has been paid to Antarctica,which is known as one of the "drivers" and "amplifiers" of global climate,and also as “wind pole”.The surface winds,as one of the important meteorological factor,are the key components of the harsh environment of Antarctica.Despite a lot of attempts made to examine extreme wind events,long-term changes and trends in Antarctic winds are still poorly understood.To address this,near-surface wind speed and wind direction observations from 19 manned meteorological stations over the Antarctic Ice Sheet and ERA5 from 1957 to 2017 are used to investigate the Antarctic wind climatology and variability during the past 50 years.The main conclusions are as follows:(1)Large and negative trends in wind speeds only occur in the coastal region of East Antarctica,while in West Antarctica they are relatively low and decreasing since the late 1950 s,and wind speeds in the Antarctic Peninsula are complex,but their overall trends are positive.The monthly wind speeds of the Antarctic Ice Sheet range from 0.1-27.1m/s,with maximum monthly wind speed recorded at Mirny station in East Antarctica and minimum at Faraday station in the Antarctic Peninsula.The averaged wind speed reaches 7.31m/s from 1957 to 2017.The meteorological stations with both seasonal and annual large wind speed values are all located in the coastal areas of the East Antarctica,and the Faraday station has the lowest one.In terms of the seasonal variations of wind speeds,most stations exhibit a clear seasonal dependence,with low values in summer and high ones may occur in any of the other three seasons.But,there is an exception,Davis Station,which has maximum wind speed in winter months,and minimum in summer months.The inter-annual variability of the near-surface wind speeds shows a “seesaw” spatial pattern,with a negative trend occurs along the coast regions of East Antarctic,and positive trend in West Antarctic.Specifically,the wind speeds show significant increased trends over thecoast regions of 0-120°E sector influenced of positive polarity of SAM.In recent decades,the Amundsen-Bellingshausen Seas Low has significantly deepened,the low-altitude cyclonic circulation has strengthened,and the southward wind on its eastern edge has increased,which in turn has led to an increase in wind speed in the Antarctic Peninsula and a decrease in West Antarctic.(2)The wind directions of the Antarctic Ice Sheet are stable general since 1957.Under the control of large scale atmospheric circulation such as katabatic and circum-polar easteries,the wind directions at the majority of sites unchanged basically except for several sites exhibiting larger changes affected by local cyclones,ocean currents and other weather disturbances.As a result,south and east winds prevail in the coastal regions of East Antarctica,and the frequencies of annual and seasonal dominant wind direction are all higher.The annual mean wind direction and the seasonal dominant wind direction in West Antarctic are also relatively stable,but the seasonal dominant wind direction among stations inthe Antarctic Peninsula is different and the frequency is also low.(3)The correlation coefficients between the wind speeds corresponding to the dominant wind directions and the mean wind speeds over the Antarctic Ice Sheet are above 0.6,and most explanations are more than 50%,indicating that the variability of the annual average wind speeds is resulted mainly from the change of wind speeds corresponding to the dominant wind directions.(4)The variations of Antarctic wind speeds in ERA5 are basically consistent with the observations.The variations of surface winds over the Antarctic Ice Sheet are discussed using ERA5 to simulate the trends of wind speeds.The results show that in spite of many differences of the spatial distribution of wind speeds in four seasons over the Antarctic Ice Sheet,the spatial patterns of the seasonal averaged wind speeds trends are basically consistent with those of annual mean wind speeds.That is to say the wind speeds in most areas of the East Antarctic are rising,even in some areas thetrends are obvious,whereas in West Antarctic they are declining generally and not obvious.The trends in the Antarctic Peninsula are complex,with both upward and downward trends.