陇中黄土高原夏季地表辐射特征分析

 利用实测辐射资料揭示了陇中黄土高原半干旱区夏季辐射特征。结果表明:该地区夏季晴天辐射比较强烈,总辐射最大瞬时值超过1 000 W\5m-2,有时甚至超过太阳常数。春小麦下垫面平均总辐射与典型晴天的日变化比值在0.6～0.8之间,净辐射比值在0.4～0.6之间,在裸地时也表现出同样的特点,表明在半干旱区云和降水对地表辐射的影响比较大。此外,日平均反射率起伏较大,最大为0.24,最小为0.11;春小麦下垫面的地表反射率为0.17,裸地为0.20。植被叶表面的水珠会导致反射率增大,而风速的增大会引起反射率的突变。受土壤湿度及太阳高度角和天气状况等因素的综合影响,不同天气条件下的地表反射率日变化呈现出比较大的差异。

Summer Land-surface Radiation Characteristic over Longzhong Region of Loess Plateau, China

The land-surface radiation characteristic over semi-arid region of the Loess Plateau is analyzed based on the radiation data observed at Dingxi Arid Meteorology and Ecological Environment Experimental Station. It is showed that the radiant intensity is very high and the maximum of instantaneous global radiation is beyond \{1 000\} W\5m~(-2), sometimes beyond solar constant in summer. The ratio of the daily average global radiation during spring wheat growth to one on a clear day is between 0.6 and 0.8, and the ratio of the daily net radiation between 0.4 and 0.6, and likewise over bare soil. In other words, it means that the cloud and rainfall can make great influence on land-surface radiation. In addition, the fluctuation of the mean daily albedo is high and the maximum and the minimum is 0.24 and 0.11 respectively during experiment. It is because the water droplet adhering to the leaf of wheat that causes the increasing of the albedo and the increasing of wind speed can induce considerable variation of the albedo. In short, the daily albedo under different types of synoptic conditions shows as different characteristic because of integrated affect which caused by soil water content, synoptic conditions and solar altitude angle.