黄土高原典型塬区冬小麦地表辐射和能量平衡特征

Study of Land Surface Radiation and Energy Balance at Winter Wheat Fields over Typical Mesa of Chinese Loess Plateau

利用2006年4～7月黄土高原陆气相互作用试验实际观测资料,分析了黄土高原典型塬区冬小麦生长过程中不同天气条件下的地表通量特征。发现在不同天气条件下辐射平衡和能量平衡特征有很大变化。地面向上长波辐射在晴天、阴天、降水天时依次减小,到达峰值时间约滞后总辐射峰值到达时间1h左右。大气向下长波辐射与地表向上长波恰恰相反,晴天量值最小,基本稳定在300W.m-2左右,阴天和降水天依次增大。潜热是能量通量的主要消耗项,在夜间也大于零,夜间感热则为负值。土壤热通量达到峰值时间滞后于净辐射峰值到达时间约1.5h,其日平均值晴天为正,阴天约为零,降水天则为负值。日平均波文比阴天大于晴天和降水天。植被覆盖度高时,土壤植被系统截留的总辐射也高。

Based on the observations of Loess Plateau Experiments from April--July in 2007, characteristics of land surface flux of the growing winter wheat in different weather conditions over the typical mesa of Chinese Loess Plateau are analyzed. The results indicate that there is large variation in the energy balance in different weather conditions. The value of the upward long-wave radiance is the largest in sunny and decreases in turn in a cloudy and rainy day. The time of the upward long-wave radiance reaches the maximum is 1 hour later than that of the total radiance. The condition of the downward long wave radiance is just contrary to the upward long-wave radiance, and it reaches a minimum of about 300 W·m^-2 in a sunny day and successive increases in a cloudy and rainy day. The latent heat flux is a main consumption part, which is positive in the night. However, the sensible heat flux is negative in the night. The time of the soil heat flux reaches the maximum is 90 minutes later than that of the total radiance. The daily average of the soil heat flux is positive in a sunny day; it is about zero in a cloudy day and negative in a rainy day. Daily average Bowen ratio in a cloudy day is larger than that in a sunny and rainy day. When the vegetation cover is larger, the total radiance intercepted by the vegetation and soil is larger too.