Evaluation of thermal roughness schemes in surface heat transfer simulations over grassland in Southeast Tibet

Abstract

Surface heat transfer processes play an essential role in the thermal effect of the Tibetan Plateau on the atmospheric system over the Northern Hemisphere. Numerical simulations are an important means used to study surface heat transfer and related atmospheric processes. The thermal roughness length (z0h) is an important parameter used to calculate surface heat transfer in numerical models. In this study, seven commonly used thermal roughness length schemes, including kB0, Zil, O63, B82, C97, C09 and Y08, were evaluated over the Southeast Tibet by using observation data over grassland and the Weather Research and Forecasting (WRF) Model. The results show that different thermal roughness length schemes exhibit large variabilities in simulating the diurnal variations in z0h and surface heat processes. Most of the schemes overestimate the z0h and sensible and latent heat fluxes while underestimate the ground heat flux. The z0h greatly affects the surface heating processes by adjusting the surface-atmosphere exchange coefficient. A large z0h value makes the land surface and the atmosphere more coupled and leads to an increase in heat and moisture transfer, and vice versa. Among these schemes, the C97 scheme performs the best for the surface heat transfer simulation over grassland in Southeast Tibet.