Abstract: 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.

Key words: Antarctica, Great Wall station, visibility, variation, period