作 者 ：张果,周广胜*,阳伏林
期 刊 ：生态学报 2010年 30卷 24期 页码：6943~6951
Keywords:surface albedo, solar altitude angle, soil water content, sunny day,
摘 要 ：基于2008年全年内蒙古荒漠草原的气象观测数据对荒漠草原地表反照率的变化特征分析发现，内蒙古荒漠草原的地表反照率在晴天呈早晚高、正午前后低的U形变化特征，降水引起的土壤含水量变化将导致地表反照率减小，云对地表反照率的影响比较复杂。荒漠草原地表反照率的月平均日变化类似于晴天条件下的日变化，大多数月份呈现早晚高正午前后低的U形变化趋势，仅在1-2月份及11-12月份呈现V形。地表反照率的季节变化较为明显。在生长季，由于存在植被覆盖使得地表反照率较低；而在冬季，地表反照率较高，特别是1\,2月份，其月均值分别为0.56和0.48，甚至高于沙漠。9月份地表反照率月均值达到最小值0.230， 7、8\,9月份地表反照率接近，分别为0.236、0.232和0.230。而且在生长季，荒漠草原的地表反照率高于退化草地、农田及麦田，低于沙漠的地表反照率，但是荒漠草原的地表反照率除7-10月份明显低于沙漠地表反照率外(相差大于0.02)，生长季的其它月份与沙漠相差不大。晴天地表反照率随太阳高度角的增大而减小，当太阳高度角大于40°时，地表反照率趋于稳定,其与太阳高度角呈指数关系。土壤含水量的增大会导致地表反照率的减小，地表反照率与土壤含水量呈指数或线性关系。根据地表反照率与这两个因子之间的单因子关系式，建立了内蒙古荒漠草原晴天地表反照率随太阳高度角与土壤含水量变化的双因子参数化公式，而且太阳高度角和土壤含水量两者共同解释了地表反照率变化的68%左右。该公式可以较好地模拟内蒙古荒漠草原晴天地表反照率的变化。该公式是否可以进一步耦合到天气或气候模式中，还需要借助更多代表性的观测资料的验证，但是本研究无疑对陆面模式中地表反照率更准确的参数化及模拟提供了参考依据。
Abstract:Dynamic characteristics of surface albedo over a desert steppe ecosystem in Inner Mongolia were studied in this paper, based on the whole year′s meteorological data of 2008. The results indicated that the diurnal variation of surface albedo over the desert steppe in Inner Mongolia presented U-shape with higher values just after sunrise and before sunset, and relatively lower midday values on sunny days. Changes of soil water content resulted from rainfall would result in the decrease of surface albedo, and the influence of cloud on surface albedo was complicated. Usually, monthly mean diurnal variation of surface albedo over the desert steppe ecosystem was similar to that on sunny days with the U-shape, however, it presented V-shape in January, February, November and December. The seasonal variation of surface albedo was apparent. In growing season, surface albedo was lower because of the growth of vegetation; but during the winter, especially in January and February, it was higher. The monthly mean values in January and February were 0.56 and 0.48, respectively, and they were even larger than that of desert. The minimum monthly mean surface albedo of the desert steppe occurred in September. The value of the surface albedo was almost a constant from July to September, which was 0.236, 0.232 and 0230 respectively. In growing season, the surface albedo over the desert steppe in Inner Mongolia was higher than that over degraded grassland, agricultural land and wheat field. Only from July to October, the surface albedo over the desert steppe was obviously lower than that over the desert (the difference value was larger than 0.02). However, in other months of growing season, it was close to the surface albedo over the desert. On sunny days, the surface albedo decreased with the increase of solar altitude angle, showing a typical exponential relationship, and it almost became a constant when solar altitude angle was more than 40°. The increase of soil water content would result in the decrease of surface albedo. The linear or exponential relationship exists between surface albedo and soil water content. Thus, based on the relationship between surface albedo and solar altitude angle as well as the relationship between surface albedo and soil water content, a two-factor parameterization formula of surface albedo affected by solar altitude angle and soil water content was developed preliminarily. And this formula could explain about 68% of the variation of surface albedo. The parameterization formula could capture well the diurnal variation of surface albedo on sunny days over the desert steppe in Inner Mongolia. This formula should be validated by more representative observation data, in order to couple it into climate models or weather models. However, it is no doubt that this study could offer useful references for the precise parameterization and simulation of surface albedo in land surface model.
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