Regional and temporal variations in arctic cloudiness

Regional and temporal variations in monthly mean cloud fraction, low-cloud type, and surface air temperature are analyzed using Hahn and Warren’s archive of cloud and other meteorological variables extracted from surface weather reports during 1972-1996. The goal of the study is to identify prominent climatic features related to arctic clouds, which can be used for developing and testing conceptual and numerical cloud models. The mean annual cycle of cloudiness is examined at three locations: Jan Mayen at 71 N in the East Greenland Sea, a region near 62 N, 125 E in central Siberia, and drifting sea-ice stations in the North Pole region. The climate of Jan Mayen is strongly influenced by the surrounding ocean: despite its position north of the Arctic Circle summer and winter temperatures differ by only 10 C. The monthly mean cloud fraction is strikingly steady and large throughout the annual cycle. Total cloud fraction is between 80% and 85% and low-cloud fraction is between 65% and 70%. The climate of Siberia has a distinctly continental character, with the monthly mean temperatures ranging from less than -35 C to almost 20 C. Monthly total cloud fraction varies between 60% and 80%, and has two maxima in April and October. Low cloud fraction is about 25% during the warmer half of the year and drops to only 5% in the winter. The climate of the North Pole has characteristics of both continental and maritime regions. During the summer the melting sea ice keeps the surface air temperature close to 0 C, much as the ocean moderates the temperature in maritime areas; yet during the winter the thick solidified ice pack behave similarly to a land surface, allowing monthly mean temperatures to dip below -30 C. The dual nature of the North Pole climate is also evident in its cloud cover. During the summer at the North Pole the cloud amount and cloud type are very similar those in Jan Mayen, and during the winter there is a strong similarity with Siberia. The regional variation in the base height and type of low clouds was also examined. During the summer over land, warmer surface temperatures were associated with a greater frequency of occurrence of cumuliform cloud types and fewer stratiform clouds. An analysis of interannual variations in monthly mean cloud fraction and surface temperature showed the following for arctic continental areas: temperature and low-cloud fraction have a strong positive correlation during the winter and a strong negative correlation during the summer. In Finland and northwestern Russia, wintertime low-cloud amount is strongly correlated with the North Atlantic Oscillation.