Study on surface layer turbulent and energy exchange in Eastern edge of the Tibetan Plateau

Abstract

Mount Emei is located in the eastern edge of the Tibetan Plateau, on the transition zone between the main body of the Tibetan Plateau and the Sichuan Basin in China. It is not only the necessary place for the eastward movement of the plateau system, but also the place where the southwest vortex begins to develop. Its special geographical location makes it particularly important to understand the turbulence characteristics and surface energy balance of this place. Based on the Platenay Boundary Layer (PBL) tower data, radiation observation data and surface flux data of Emeishan station on the eastern edge of Tibetan Plateau from December 2019 to February 2022, the components of surface equilibrium are estimated by eddy correlation method and Thermal Diffusion Equation and Correction (TDEC) method, the characteristics of surface energy exchange in Emeishan area are analyzed, and the aerodynamic and thermodynamic parameters are estimated. The results show that the annual average value of zero-plane displacement d is 10.45 m, the annual average values of aerodynamic roughness Z0m and aerothermal roughness Z0h are 1.65 m and 9.95 m, respectively, and the annual average values of momentum flux transport coefficient CD and sensible heat flux transport coefficient CH are 1.58×10-2 and 3.79×10-3, respectively. Under the unstable stratification, the dimensionless three-dimensional wind fluctuation variance in Emeishan area can better conform to the 1/3 power law of Monin-Obukhov similarity theory. In the near neutral case, the dimensionless velocity variances in the u, v and w directions are 2.412, 2.181 and 1.125 respectively, and the dimensionless velocity variances in the horizontal direction are greater than those in the vertical direction. The diurnal and seasonal variations of each component of surface balance are more obvious. The dominant position of sensible heat flux and latent heat flux during the day varies with seasons. The latent heat flux is dominant in summer and the sensible heat transport is dominant in winter. The diurnal variation range of surface albedo in Emeishan area shows the characteristics of large in the morning and small in the afternoon, which is an asymmetric "U" shape. Its value is between 0.04-0.08. The surface albedo in summer and autumn is higher than that in Emeishan. The influence of underlying surface on surface reflectance is much greater than other factors such as altitude, longitude and latitude.