干旱区绿洲地表反照率不对称观测研究

OBSERVATION STUDY ON DIURNAL ASYMMETRY IN SURFACE ALBEDO OF OASIS IN ARID REGION

利用"绿洲系统能量与水分循环观测试验"2005年第一阶段资料分析发现,绿洲的地表反照率并不是呈现关于太阳高度角的典型对称分布,早上的地表反照率略大于相同太阳高度角的下午,在太阳高度角30°附近早上比下午平均大0.031,约为平均反照率的13.3%。白天风速较小、风向变化不定的风场和当日的土壤湿度差异对地表反照率不对称的影响较小。早晚地表反照率差异主要是由于绿洲内空气较为湿润、夜晚风速较小、气温下降形成的露水在早上增大对太阳辐射的散射造成的。而在日出后露水迅速蒸发,在太阳高度角为40°～50°,上午和下午的地表反照率基本重合。

By utilizing data observed in the first phase of ＂The Oasis System Energy and Water Cycle Field Experiment＂ in 2005, surface albedo of oasis was analyzed. Results showed that surface albedo is asymmetric about the solar elevation angle. Surface albedo in the early morning is bigger than that in the late afternoon. Morning/afternoon surface albedo difference is about 0.031 which is 13.3% of the average surface albedo at the 30° solar elevation angle. The diurnal asymmetry of surface albedo is less influenced by the diurnal difference of soil moisture and the wind field which has the small speed and irregular direction. Because of the plenty of vapor, the low temperature and the small wind speed at night, the dew easily formed in oasis. The surface albedo difference between the morning and the afternoon is mainly due to the dew which increased the capability of scatter to solar radialion in the morning. After sunrise the dew quickly evaporated and the albedo began to be symmetric about the solar elevation angle between 40° and 50°.