我国北方不同类型下垫面地表反照率特征

Study on land-surface albedo over different types of underlying surfaces in North China

地表反照率反映了地面对太阳辐射的反射能力,在地表能量平衡中起着非常重要的作用,本文利用"中国北方协同观测"的资料,分析了不同下垫面10个站点7-9月的反照率变化特征和对降水的响应,并讨论了榆中、通榆草地、通榆农田、密云、玛曲和锦州站地表反照率与太阳高度角和土壤湿度的关系,结果表明:反照率的相对关系是东北干旱草甸>西北高寒草甸>西北绿洲农田>黄土高原自然植被>东北半干旱草甸>东北农田>东北果林,并且反照率基本上和降水对应,降水量大的站点反照率小,降水量小的站点反照率大,反照率的日变化曲线分为早晚对称型,早上比较大、中午下午比较小和晚上最大、早上最小的不对称型三种,选取的6个观测站反照率的谷值一般出现在降水日,峰值一般出现在没有降水、太阳辐射比较强的日子,地表反照率随着太阳高度角的增大而减小,当太阳高度角大于40°时,地表反照率基本不变,榆中和通榆农田地表反照率随着土壤湿度增大减小较明显,其次是通榆草地,玛曲、密云和锦州地表反照率随着土壤湿度变化不明显。

Land-surface albedo reflects the ability that land surface reflects solar radiation and plays a very important role in surface energy balance. By picking 10 different underlying surfaces including bare soil, cropland and grassland, the differences in the diurnal variation of land surface radiation and energy processes over North China are investigated using the data measured during July and September, 2008, provided by the Experimental Co-observation and Integral Research in Semi-arid and Arid Regions over North China, the characteristic of land-surface albedo and the response to precipitation are analyzed, and the relationships between land-surface albedo and solar altitude angle and soil humidity are studied. According to the average albedo, the sequence of albedo over all the underlying surfaces are arid meadow in the northeast of China〉alpine meadow in the northwest of China〉oasis farmland in the northwest〉natural vegetation on the Loess Plateau〉semi-arid meadow in the northeast of China〉farmland in the northeast of China〉fruit bearing forest in the northeast of China. And the albedo is smaller when the precipitation is much while it is bigger when the precipitation is less on the whole. The diurnal variation curves of albedo have three types： symmetric type, bigger in the morning and smaller in the noon and afternoon, biggest in the afternoon and smallest in the morning. In the selected 6 stations, the valley of albedo basically occurs on rainy days and the peak occurs on days which are not rainy but have strong solar radiation. The land-surface albedo decreases with the solar altitude angle increasing and tends to remain when the solar altitude angle is bigger than 40° The land-surface albedo decreases obviously with soil moisture increasing in Yuzhong and farmland of Tongyu, then the grassland of Tongyu. And the land-surface albedos of Maqu, Miyun, Jinzhou have no significant change with the soil moisture.