南极长城站能见度变化分析

利用南极长城站1986—2012年能见度人工观测资料,分析了能见度的变化特征和趋势。结果显示,高于10 km能见度出现频率为61.0%,低于1 km的频率为8.0%。11—3月能见度较好,6—10月能见度较差;海雾和降水是夏季能见度降低的主要原因,冬季则主要归因于频繁的降雪、吹雪或雪暴等灾害性天气。10 km能见度发生频数有显著减小倾向,10 km能见度呈上升趋势,且冬季的上升速度最快,大雾、吹雪和降雪减少是主导冬季能见度升高趋势的重要因素。长城站能见度显著的天气尺度周期为2.1—8.3 d,年际变化周期为2 a、4.1 a和6.9—8.2 a,又以4.1 a最为显著。2012年开展的能见度自动观测实验表明,20 km范围内的自动观测精度较高,适用于长城站的连续监测。

ANALYSIS OF VISIBILITY VARIATION AT GREAT WALL STATION,ANTARCTICA

Visibility variations at Great Wall station (GWS) were investigated using manual observation data collected from 1986 to 2012. High visibility (≥10 km) and low visibility (0–1 km) accounted for 61.0% and 8.0% of records, respectively. The visibility at GWS showed clear seasonal variation with best visibility in November–March and worst visibility in June–October. Sea fog and precipitation were the main causes of low visibility in summer, while frequent severe weather including heavy snowfall, blowing snow, and blizzards were responsible for low visibility in winter. The frequency of low visibility decreased significantly from 1986 to 2012, and the annual and four-season average visibilities all followed a significant trend towards higher visibility, which was strongest for winter. Less frequent fog, blowing snow, and snowfall events contributed to the trend towards higher winter visibility. Variation in visibility at GWS was significant at synoptic (2.1–8.3 days), annual, and inter-annual scales (2 years, 4.1 years and 6.9–8.2 years), with the most significant variability at an inter-annual scale of 4.1 years. Automatic observation of visibility was carried out in 2012, and the results showed that automatic observation could be effective for the future continuous monitoring of visibility at GWS.