Spatial variations in snow cover and seasonally frozen ground over northern China and Mongolia, 1988-2010

This study investigates the spatiotemporal variability of snow cover and seasonally frozen ground in northern China and Mongolia during 1988-2010 with passive microwave remote sensing records. We used the Goodison snow algorithm, adapted by introducing an additional soil freeze/thaw indicator to improve its efficiency in mountainous areas, and soil freeze-thaw algorithm to estimate snow cover onset, duration, ablation and, for the first time, interval between snow cover ablation and thawing of seasonally frozen ground. Snow cover onset, duration, and ablation tended to vary systematically from high to low latitudes, and to trend toward early/long/late in elevated areas. The ablation-thawing interval varied from low to high latitudes/elevations, and from dry to relatively humid areas, being shorter (< 2 weeks) in the north and elevated areas but longer in some cold-dry and plain-mountain adjacent regions. During 1988-2010, snow cover showed a later/earlier trend of the onset/ablation on the western Tibetan Plateau and a belt from northeast China to central Mongolia, with trends being stronger in spring than in autumn. The time of snow cover ablation was negatively correlated with maximum temperature in the northern study area, indicating that temperature mainly advanced snow melting in spring. However, no significant relationship between temperature and the interval was observed, suggesting that other unknown factors impact the interval. Furthermore, in the north and on Mt. Changbai the interval changed by < 2 weeks, whereas changes were larger in cold-dry and plain-mountain transitional areas, indicating changes of Earth surface systems in those areas.