An Investigation of Temporal and Spatial Variations of 1988～ 1998 Snow Cover over the Northern Hemisphere
1988～1998年北半球积雪时空变化特征分析

A NOAA satellite-derived dataset of the weekly snow cover for 1988- 1998 was used in this study to describe its temporal and spatial variations. A counted number of the weeks (CNW) with snow cover at each grid point is defined for a year or a season to quantitatively measure accumulation of the snow cover. Detailed analysis based on the computed 10-year CNW data shows a remarkable interannual variation for the snow cover over the Northern Hemisphere during last decade. Key areas for the interannual variation are located in the Tibetan Plateau, the Mongolian Plateau, the Alps and central and western regions of North America, and the Tibetan Plateau is the most important region with the largest interannual variability in CNW. There are two patterns relating the variation of snow cover over the Tibetan Plateau to that of other regions. One is the in-phase pattern between the Tibetan Plateau and other regions (say, Europe, and far eastern region of Russia), and this pattern has an obvious ascending trend over last decade, indicating a continuous increase of snow cover over the Tibetan Plateau since 1988. The other pattern is characterized by an out-of-phase relation between over the Tibetan Plateau and over Europe, the Mongolian Plateau, North-eastern China, but by an in-phase relation between over the Tibetan Plateau and over the central Asia, and this pattern has a certain kind of interannual oscillation.