Tropical cyclone low-level wind speed, shear, and veer: sensitivity to the boundary layer parameterization in WRF

Abstract. Mesoscale modeling can be used to analyze key parameters for wind turbine load assessment in a large variety of tropical cyclones. However, the modeled wind structure of tropical cyclones is known to be sensitive to the boundary layer scheme. We analyze modeled wind speed, shear, and wind veer across a wind turbine rotor plane in the eyewall and rainband region. We further assess the sensitivity of wind speed, shear, and veer to the boundary layer parameterization. Three model realizations of typhoon Megi over the open ocean using three frequently used boundary layer schemes in the Weather Research and Forecasting model are analyzed. All three typhoon simulations reasonably reproduce the cyclone track and structure. The boundary layer parametrization causes up to 21 % differences in median hub height wind speed between the simulations. The simulated wind speed variability is further dependent on the boundary layer scheme. The modeled wind shear is smaller or equal to the current IEC standard regardless of the boundary layer scheme for the eyewall and rainband region. While the surface inflow angle is sensitive to the boundary layer simulation, wind veer in the lowest 400 m of the atmospheric boundary layer is less affected by the boundary layer parametrization. Simulated wind veer reaches values up to 1.8 × 10⁻² ° m ⁻¹ (1.1 × 10 ⁻² ° m ⁻¹) in the eyewall region (rainband region) and is relatively small compared to moderate wind speed regimes. On average, simulated wind speed shear and wind veer are highest in the eyewall region. Yet strong spatial organization of wind shear and veer along the rainbands may increase wind turbine loads, due to rapid coherent wind profile changes at the turbine location.