The Influence of Bare Ground Thermal Roughness Length Parameterization on the Simulation of Near‐Surface Air and Skin Temperatures Over the Tibetan Plateau

Abstract

AbstractAn observation‐based parameterization of thermal roughness length (TRP) for bare ground has been implemented in the Weather Research and Forecasting model. This scheme introduces a temperature scale to account for the impact of atmospheric stability. The effect of the TRP scheme is evaluated by comparing simulations with the default and with the implemented one for the Tibetan Plateau (TP) region. We find that the newly implemented scheme generally shows remarkable improvement in simulating the nighttime near‐surface 2m air temperature (T2) and daytime surface skin temperature (TSK), with a reduction in cold biases. The newly implemented scheme directly leads to weakened sensible heat release to the atmosphere in the daytime, thereby increasing energy storage in the land. These changes enhance snow melting in spring and reduce snow accumulation in autumn. Due to reduced snow cover and decreased albedo in the two transitional seasons, more solar radiation is absorbed by the land surface, leading to higher TSK and T2. In summer, the snow albedo feedback plays a minor role when there is minimal snow cover. In winter, the solar radiation is weak, and the atmosphere is relatively stable. Consequently, the warming effect due to the newly implemented scheme is more remarkable in the transitional seasons than in summer and winter. This work demonstrates the importance of the TRP in simulating T2 and TSK in the coupled atmosphere‐land model, and reveals that the influence of this scheme on T2 and TSK over the TP region is mainly associated with snow‐albedo‐shortwave radiation processes.