Dynamics Of Desert Steppe Surface Albedo In Inner Mongolia And Its Effects On Land-atmosphere Fluxes

Desert steppe is located in the transitional zone from typical steppe to desert region, it is very important in land-atmosphere interaction due to its rapid changes in land surface parameters. Especially, its surface albedo determines the absorption of solar radiation, and controls directly the distribution of absorbed solar radiation among latent heat flux, sensible heat flux and soil heat storage, etc. Thus, the surface albedo is very important for the accurate simulation of land– atmosphere fluxes.At present, land surface parameterization scheme of sparse vegetation in meso-scale models has not drawn more attention yet. In this thesis, the dynamic characteristics of surface albedo over desert steppe and its parameterization would be studied, in terms of the whole year's data of 2008 from eddy covariance tower and meteorological tower. Also, the effects of this parameterization scheme on land– atmosphere fluxes, including sensible and latent heat fluxes, would be discussed based on NOAH land surface model. The main results were listed as follows:(1)Diurnal patterns of sensible and latent heat fluxes over the desert steppe were single kurtosis, which were similar to the diurnal pattern of net solar radiation, but their maximum values lagged about one hour. The patterns of sensible and latent heat fluxes and net solar radiation were affected by precipitation. Also, sensible heat fluxes were obviously affected by net solar radiation, but latent heat fluxes were more sensitive to precipitation. In addition, soil water content played a major role in the change of latent heat fluxes. When heavy rain occurred, both of sensible and latent heat fluxes were smaller. If sunny day took place after the heavy rain, latent heat fluxes were larger.(2) Surface albedo over the desert steppe in Inner Mongolia presented U-shape with higher values just after sunrise and before sunset, and relatively lower midday values on sunny days. Changes of soil water content would result in the decrease of surface albedo, and the influence of cloud on surface albedo was complicated. On sunny days, the surface albedo decreased with the increase of solar altitude angle, and it almost became a constant when solar altitude angle was more than 40°. The surface albedo had a typical exponential relationship with solar altitude angle. The linear or exponential relationship existed between surface albedo and soil water content. Considering the effects of solar altitude angle and soil water content, a two-factor parameterization formula of surface albedo was developed preliminarily. This formula could explain about 68 percent of surface albedo variation.(3)Based on the parameterization scheme of surface albedo over desert steppe, NOAH land surface model could capture well the diurnal variation of the surface albedo over the desert steppe in Inner Mongolia. By comparison, the application of the desert steppe surface albedo parameterization scheme improved the simulation of upward solar radiation and sensible heat fluxes, although the simulation of latent heat fluxes was not significantly improved. This study might be helpful for the development of the regional climate and weather models.