The Analysis Of The Surface Energy Budget In Semi-arid Areas In Chinese Loess Plateau

Semi-Arid Climate and Environmental Observatory of Lanzhou University (SACOL) is located in southwest China's Loess Plateau and it is typically semi-arid area. As the only uninterrupted observation CEOP site in Loess Plateau region, since the foundation in September 2005, SACOL has achieved a lot of valuable data.In this paper, we use the conventional meteorological data of the boundary layer, momentum flux, CO₂ and H₂O flux, the radiation components and the latent heat and sensible heat flux of SACOL from May 1st, 2006 to April 30th, 2007 to analyze the average field characteristics, the characteristics of turbulence and the change law of radiation and the surface energy balance problems.Our conclusions are as follows:1. Southeast winds and northwest winds prevail in SACOL all the year round; the diurnal variation of horizontal wind speed and vertical wind speed, friction wind speed show good consistency; humidity and atmosphere pressure have obvious diurnal variation characteristics; the change laws of CO₂ concentration and fluxes of CO₂ are basically similar, presenting a single peak-valley-type; the ecological system in SACOL is weak; consequently, the effect of vegetation photosynthesis and absorption upon the concentration of CO₂ in this region is not obvious.2. Because the elevation of SACOL is higher than plain areas and there are relatively more sunny days, the resources of sunshine in SACOL region is rich ; the surface albedo's seasonal change is obvious, and its value is between that of Zhangye oasis and Dunhuang Gobi which are located in the northwest areas. The albedo is affected significantly by surface vegetation, snowfall and other weather conditions. The atmospheric counter radiation and terrestrial long-wave radiation change with the air temperature and surface temperature significantly.3. The diurnal variation of soil temperature performs like sine curve. The peak time lags with the increase of soil's depth, and the amplitude of diurnal variation decreases with depth. The precipitation and soil moisture have a very good correlation; and the moisture variation of deep soil has a certain phase lag compared to shallow soil.4. The energy closure rate is gradually increasing from morning to afternoon. The main reason why energy imbalance is more serious at night is the low intensity of turbulence. In SACOL area, as the air humidity is very low, sensible heat flux is much larger than latent heat flux. The annual average ratio of Bowen is 1.42.5. By using the observation data from June to August 2003 of Tongyu Observation which is also located in the semi-arid area, we analyze its surface energy balance condition and make comparison with SACOL: the net radiations of the two places are basically the same, but latent heat and sensible heat flux of the two places are different obviously. Although they are located in the same semi-arid area, owing to different humidity condition in summer, their surface energy distributions are quite different.