Summer heat transfer over a Gobi underlying surface in the arid region of Northwest China

Using the routine meteorological measurements and supersonic measurements at Dunhuang Gobi site in June 2004 and August 2008 as an example,This paper analyses the general process of summer heat transfer and its characteristics over a Gobi underlying surface in the arid region of Northwest China.Observation qualities of turbulent fluxes and measured surface energy closure are first evaluated,indicating that the system in the site measures well during the daytime overall.The typical diurnal variations of surface energy fluxes in summer show that the latent heat flux is generally little and can be ignored.In the daytime,both downward solar radiation and upward longwave radiation near surface are strong,and surface net radiation is mainly transformed into sensible heat flux(e.g.,mean surface net radiation and sensible heat flux at noon at Dunhuang Gobi site can reach more than 380 W·m-2 and 250 W·m-2,respectively).Soil releases energy to balance surface radiation cooling in the nighttime,and sensible heat flux is a little less than 0.The frequently occurred free convection activity near-ground is found in the daytime,which influences the observation quality of momentum flux.It can effectively transfer near-ground heat into upper air and contributes to the super depth of the atmospheric boundary layer.The characteristics of momentum roughness length and thermodynamic roughness length over the Gobi surface are further researched.The momentum roughness length at Dunhuang Gobi site is determined as 0.6 mm.The thermodynamic roughness length is an order of magnitude lower than the momentum roughness length,which agrees with the primary understanding of thermodynamic transport characteristics over the arid region.