Observational Experiment of Land-Atmosphere Interactions in Typical Semi-arid Areas: A Case Study in Dingxi

Land surface site data is one of the key aspects of land-atmosphere interaction, and one of the validated criteria for land surface model results. It also provides data for the land surface assimilation system. The semi-arid area of the Loess Plateau is not only an ecologically fragile area, but also a strongly coupled area between land and air. Land surface processes in this area have an important impact on weather and climate. In order to get a comprehensive insight into the land characteristics we analyzed observational data of land surface processes with quality controlling at different temporal scales at Dingxi Station. The results show that the monthly surface energy closure of Dingxi Station is 0.5~0.9, and the monthly average closure is 0.7, which is in the normal range but slightly lower than the daily average closure. On the daily scale, the average diurnal variation of land surface characteristics is still consistent with that of sunny days. In the cold season, the surface energy is predominantly sensible heat. The soil heat flux is almost equal to sensible heat, and the latent heat is little in the daytime. In the warm season, the latent heat increases significantly and has the same order of magnitude with sensible heat, and the heat flux of soil is evidently smaller than that of the two. The soil active layer is 20cm depth. On the seasonal scale, the turbulent flux is manifestly different between that of the in wet season (May-October) and dry season (November-April). The sensible heat flux and latent heat flux in the wet season are of the same order of magnitude, while it is dominated by sensible heat flux and there is little latent heat in the dry season.