Surface Energy Balance In Semi-arid Region

Using the continuous observation data from May2006to December2008at the Semi-arid CLimate and Environment Observatory of Lanzhou University(SACOL), and from January2007to December2008at the he Tongyu semi-arid cLimate and environment Observatory (the degraded grassland station and the farmland station) and US-Aud station and US-ARM station at the North American semiarid region,surface radiation characteristics and the surface energy balance characteristics at SACOL were analyzed, but also is compared with the Tongyu semi-arid climate and environment Observatory (the degraded grassland station and the farmland station) and US-Aud station and US-ARM station at the North American semiarid region, comparing the characteristics and differences of the gas exchange process in the underlying surface.(1)The radiation components at SACOL has significant diurnal variation with a peak, but there are some differences in the magnitude of changes, the range of shortwave radiation is relatively large, and the range of the Long-wave radiation is relatively small. Each radiation component at SACOL showed a significant variation in the average monthly variation in radiation values showed a single peak, the magnitude of each radiation component are not similar, and no significant difference between years. from the December to May the mean radiation increases, and from July to October the mean radiation decreases gradually.(2) Diurnal variation of surface albedo at SACOL takes on "U" shape, the daytime surface albedo is between0.2to0.3. Rain and snow will cause great impact on the surface albedo, the surface albedo in sunny days is high at the noon and Low in the evening, was Low in the evening and high in the morning after the rain, and is high in the morning and Low in the evening after the snow. Surface albedo and the shallow soil moisture are negatively correlated, fitting an exponential decay curve with the increase of soil depth, the correlation coefficient decreases.(3)The latent heat flux, the sensible heat flux and net radiation in the four seasons exhibit the same diurnal variation, the diurnal variation is obvious, the performance of each component are after sunrise gradually increases and reaches a maximum at noon, followed by a rapid decrease. The diurnal variation of soil heat flux is also obvious, but the magnitude of the change is relatively small. The distribution ratio of the sensible heat flux and the latent heat flux showed significant anti-phase changes in the growing season, the latent heat flux is greater than the sensible heat flux, while in non-growth season, is relatively small in the rain; precipitation could affect near-surface distribution of energy through the impact of the latent heat flux; The influence of precipitation on the surface heat flux is small. Bowen ratio in spring and winter significantly greater than0, and summer and fall due to the distribution and intensity of precipitation changes in the vicinity of1.0.(4) Without considering the soil heat storage at SACOL, the energy closure rate is0.64, the intercept is21.98W/m2, while considering the soil heat storage, the energy closure rate is0.68, the intercept is29.34W/m2, we must consider the soil heat storage if calculating the energy closure rate.(5) Comparing the average albedo changes at SACOL, Tongyu grassland station, Tongyu cropland station (Tongyu-nt), US_Arm stations and US_Aud station from November to March, in addition to SACOL the albedo curve is "L" shaped, the rest of the sites were "U" shaped.(6) Whether semi-arid region over the Loess Plateau and semi-arid region in northeast China or the semi-arid region in north America,sensible heat flux was dominant in the energy partitioning, accounted for33-38%of the net radiation, latent heat flux accounted for13-29%, while the surface heat flux was Lowest only7-19%. The monthly precipitation associated with the sensible heat flux and latent heat flux strongly, the abundant rainfall of the month, the sensible heat flux is relatively small, the latent heat flux is significantly larger than the sensible heat flux, and less precipitation month, sensible heat flux was significantly greater than the latent heat flux, the latent heat flux is relatively small.(7) Comparing the SACOL, Tongyu grassland station, Tongyu cropland station (Tongyu-nt), US_Arm stations and US_Aud station, you can find the surface energy is not closed, the no-closed rate is from0.23to0.38, while the closure rate at Tongyu cropland station can be seen close up0.5points Lower than the grass station, showing that about5percent of the energy Loss in the vegetation canopy.