Abstract
The purpose of this study is to make an exploratory investigation of the interannual variability of winter snow cover in the Northern Hemisphere, using the satellite-derived monthly snow cover data from 1967 to 1987. The data set was supplied in digitized form by the National Oceanic and Atmospheric Administration/National Environmental Satellite Data Information Service (NOAA/NESDIS).
An empirical orthogonal function (EOF) analysis is made to find the typical pattern of snow cover variations during winter. The first component of the EOF (EOF1), which represents 46.6 % of the total variance, shows concurrent snow cover patterns between the Eurasia and North America. The time series of the EOF1 is similar to that of total winter snow cover in the Northern Hemisphere. The second component of the EOF (EOF2), which represents 23.6 % of the total variance, shows a negatively correlated pattern between the eastern and western parts of the Eurasia, and also shows a negatively correlated pattern between eastern Eurasia and North America. This EOF2 shows the importance of subcontinental-scale snow variations as a climatic control to a large continent.
We examined the time series of mean snow cover for the representative areas depicted in the EOF patterns to investigate the persistency of snow cover in more detail. Snow cover features for a specific years (eg. a heavy or light snow years) are likely to be sustained during December to February and disappear in March. The significant decrease of the snow cover area from February to March in a heavy snow year is prominent in eastern Eurasia. Two key regions were selected which represent continental-scale snow variation: One is the eastern part of Eurasia and the other is North America. The time series of the two key regions show an apparent 1-year lag relationship of heavy snow years; winters with extensive snow cover over Eurasia tend to be followed by relatively heavier snow cover over North America during the succeeding winters.
