春末黄土高原半干旱区地表能量闭合的观测研究

利用兰州大学半干旱气候与环境监测站的连续观测数据,分析了该站的数据质量情况和黄土高原半干旱区的近地层湍流通量特征及地表能量平衡能量闭合状况.结果表明:兰州大学半干旱气候与环境监测站(SACOL)湍流通量的平均时间取30min为宜.该站利用EdiRe获得的湍流通量较TK2和CR5000数据自动记录器输出的湍流通量结果要好.黄土高原半干旱区近地层湍流能量与地表含水量状况明显相关,地表干燥时感热通量处于主导地位,接近于干旱区的特征;地表湿润时感热通量和潜热通量则相当,接近于湿润地区的特征.地表能量平衡分析表明,兰州大学黄土高原半干旱环境监测站观测的地表能量闭合度高达85%,与已有的观测相比,能量闭合情况属于较好水平.

Observational Study of the Surface Energy Closure in the Semi-Arid Regions of Loess Plateau in Late Spring

The characteristics of surface layer's turbulent flux, surface energy balance and energy closure in the semi-arid regions of Loess Plateau are analyzed, using the data observed from the Semi-Arid Climate and Environment Observatory of Lanzhou University. The observatory is about 48 km away from the center of Lanzhou city, situated at the southern bank of the Yellow River in Gansu province (35.57°N, 104.08°E). It is situated on the China-Loess Plateau, about 1 965.8 m above sea level. The topography around the observatory is characterized by the Loess Plateau consisting of plain, ridge and mound, etc, with the elevation ranging between 1 714～2 089 m. There is loess soil in the terrace, ridge and mound. The terrain where the measurements are carried out is flat and covered with short glass. The annual mean temperature is 6.7 ℃, the January mean temperature is -8 ℃ and the July mean temperature is 19 ℃. The annual mean precipitation is 381.8 mm, and the relative humidity is 63%. In this article, using the 11-day observation from May 21-31, 2006, the data quality and the characteristics of surface layers turbulent fluxes, surface energy balance and energy closure in the semi-arid region of Loess Plateau are analyzed. The results display that: the average period of 30 min～1 h is the best time scale in the observatory. The output of turbulent fluxes is the best by using the soft of EdiRe, as compared with using the soft TK2 and CR5000 automatic data recorder. Obviously, there is a correlation between the turbulent flux of surface layer and the surface moisture condition. In the dry period, the surface sensible heat flux is dominant, showing the characteristics of arid region; in the wet period, sensible heat flux is equal to latent heat flux, similar to the humid areas. The surface energy balance closure rate in the observatory is as high as 85%, which is better level as compared with other observations.