多年冻土区与季节冻土区地表反照率对比观测研究

Comparatively observational study of the surface albedo between the permafrost region and the seasonally frozen soil region

利用多年冻土区唐古拉气象站与季节冻土区那曲毕节气象站2008年辐射、土壤未冻水含量及积雪等数据,对两种冻土类型下垫面上的地表反照率进行分析研究,得出两站地表反照率均呈现冬春季较大,夏秋季较小的规律,并且,积雪使地表反照率形成极大值,最大极值接近0.9。唐古拉站的地表反照率整体上比毕节站大,年平均地表反照率分别为0.38和0.31。地表反照率月较差(每月日平均地表反照率最大值与最小值的差值)冬季毕节站高于唐古拉站,而夏秋季节则相反。晴天,两站地表反照率均呈现"U"形,表现出早晚大、中午小,春、夏、秋、冬各季节典型晴天的地表反照率日平均值唐古拉站分别为0.23、0.20、0.20和0.25,毕节站为0.26、0.21、0.22和0.29。此外,讨论了两站太阳高度角和土壤湿度对地表反照率的影响,得出两站地表反照率随太阳高度角的增大均呈现e指数衰减趋势,土壤湿度与地表反照率呈负相关关系,且降雨对地表反照率的变化影响较大。

Albedo is an important parameter in the study of land surface process. The data of radiation, soil moisture content, snowdepth, and so on, at the Tanggula meteorological site （TGLMS） and the Bijie site （BJMS） in 2008 were used. The albedoes in the permafrost region and seasonally frozen soil region were analyzed. The albedoes of the two sites were bigger in spring and winter but smaller in summer and autumn. The albedo extreme values were caused by snow cover with the maximum extreme value close to 0.9. The albedo at TGLMS was greater than the one at BJMS, and the yearly averaged albedo were 0.38 and 0.31 in these two sites, respectively. The monthly albedo difference （the difference between the daily maximum value and the daily minimum value in every month） at BJMS was bigger than that at TGLMS in winter, but it was inverse in summer and autumn. In typical clear days, the diurnal variations of albedo took an ＂U＂ shape, and it indicated that the albedo was bigger in morning and evening but smaller at noon. The daily average albedo on the typical clear days of spring, summer, autumn and winter were respectively 0.23, 0.20, 0.20 and 0.25 at TGLMS, and the ones at BJMS were 0.26, 0.21, 0.22 and 0.29, respectively. Moreover, the relationships between the albedo and solar altitude angle and soil moisture content were discussed. The albedo exponentially decreased with the increasing solar altitude angle. The albedo negatively correlated to the soil moisture content and was greatly influenced by the precipitation.