陇中黄土高原半干旱草地地表反照率的变化特征

Change Features of Surface Albedo of Semi-Arid Grassland over the Loess Plateau of Middle Part Gansu

利用2010年兰州大学半干旱气候与环境观测站(SACOL)全年的观测数据,对陇中黄土高原半干旱草地的地表反照率年变化及其在典型天气条件下的变化特征进行研究。结果表明,该地区半干旱草地的地表反照率呈冬半年高、夏半年低的特点,年平均地表反照率为0.21,高于绿洲地区,低于半干旱农田区;地表反照率的日变化明显受天气条件的影响:晴天时呈早晚高、中午低的特征,阴天时日变化很小;降雨后地表反照率先降后升,而降雪后则先升后降;沙尘天气过程中,地表反照率比晴天有所增加。晴天时地表反照率还存在明显的不对称现象,即相同太阳高度角时,上午地表反照率大于下午,这种差异与浅层土壤湿度的变化具有较好的一致性。

The annual variation of the surface albedo of semi-arid grassland, and its variation characteristics un- der typical weather conditions over the Loess Plateau of middle part Gansu were analyzed by using the observa- tion data of Semi-Arid Climate Observatory and Laboratory of Lanzhou University （SACOL） in the whole year of 2010. The results show that： The surface albedo of semi-arid grassland over the Loess Plateau of middle part Gansu is higher in winter half year than that in summer half year, and the annual average surface albedo is 0.21, which is higher than that in oasis regions, but lower than that in the semi-arid farmlands. In addition, weather conditions obviously have impacts on the diurnal variation of the surface albedo. In sunny days, the surface albe- do is higher in morning and evening but relatively lower at noon, while it has little variation in cloudy days; The surface albedo firstly decreases and then increases after rainfall, while firstly increases and then decreases after snowfall. Moreover, the surface albedo is a little higher in dust weather than that in sunny days. Surface albedo is significantly asymmetric in sunny days, namely the surface albedo is higher in early morning than that in late afternoon at the same solar elevation. The difference has good agreement with the variation of shallow soil mois- ture. The results of this study have a certain scientific value in determining the surface albedo, verifying and im- proving models＇ ability to simulate weather and climate.