Study of the Temporal and Spatial Distribute of the Snow Cover in the Tianshan Mountains,China

Based on the remote sensing snow cover data from 2000 to 2006 over the Tianshan Mountains in China,the annual change of snow distribution,the snow distribution change with elevation,the snow cover frequency and snow line altitude change are studied.The result shows that:1)the snow cover accumulates from autumn and melts in spring,the snow cove extent of January and February is the maximum,but in July and August is the minimum,the proportion of the winter snow cover extent exceeds by 50%;2)the snow cover extent has a little increasing tendency.Seasonally,the snow cover extent is increasing in winter,however,in spring,summer and autumn the snow cover extent does not show obviously change trend.The snow cover extent changes with elevation,it increases with elevation below 4 000 m and decreases with elevation above 4 000 m.At the altitude of 2 000 m the increasing trend reaches the maximum;3)there are five large snow cover areas,with the maximum snow cover ratio over 70%.Spatially,in the middle of Tianshan Mountains snow cover is the most,followed by that in the east of Tianshan Mountains.Below 3 000 m,there is less snow cover frequency,but above 3 000 m the frequency increases obviously.Monthly snow cover frequency is very often above 4 000 m,especially in December,January and February;above 2 500 m,the snow cover frequency is more than that below 2 500 m in October,November March and April;the snow cover frequency is more above 3 000 m than that below 3 000 m in May,June,July,August and September;4)taken the elevation where the snow cover ratio is 40% as the snow line altitude,the average snow line altitude is about 2 875 m,and snow line altitude in summer is above 4 000 m but in winter it is about 1 500 m.