Effects of a Modified Sub-grid-scale Terrain Parameterization Scheme on the Simulation of Low-layer Wind over Complex Terrain

Due to the limited representation of observation over complex terrain, high resolution model becomes a favorable tool. Fine numerical simulation of wind field is quite important for micro-siting wind farms and wind energy resources assessment, especially in the complex terrain area. The accuracy of low-layer wind simulation over mountain area is one of the difficulties and key points in the field of wind energy research. The state-of-the-art WRF (Weather Research and Forecasting) model is one of the most widely used mesoscale numerical weather models for wind energy assessment in recent years. However, effects of sub-grid-scale topographic shape on surface wind field are not considered. With the new WRF version 3.4.1, a sub-grid-scale terrain parameterization scheme named Jiménez scheme is added into the YSU (Yonsei University) planet boundary layer parameterization scheme. The Jiménez scheme is designed aiming to reduce the systematic error of wind speed overestimation over valleys or plains and underestimation over hills conversely. However, correction effects of original WRF simulated 10 m wind speed by Jiménez scheme show great differences under different horizontal resolutions, particularly when over high hills. A series of sensitive numerical experiments are carried out under windy days for the Taihang Mountains in the west of Beijing-Tianjin-Hebei area. The main purpose of these experiments is to address some of issues regarding Jiménez scheme and try to solve the existing problems by establishing a relationship between the key topographic parameter C_t and the model grid spacing(dx/dy) to fit different numerical simulation for high resolution based on secondly SRTM topographic dataset. The simulated 10 m wind speed results of WRF without Jiménez scheme, with original Jiménez scheme and modified Jiménez scheme version are compared with observations of 3 automatic weather stations during the MOUNTAOM (MOUNtain Terrain Atmospheric Observations and Modeling) campaign which is prepared for 2022 winter Olympic Games. Results show that the modified Jiménez scheme can partially correct the error of the original Jiménez scheme at lower and higher resolutions. The simulated 10 m wind speed near the ground by modified version is closer to the actual condition. The correction method for Jiménez sub-grid-scale terrain scheme can provide reference for high resolution wind simulations over complex terrain and help users to obtain more detailed information on the surface wind field for wind energy related researches and applications.