Vertical Eddy Diffusivity Parameterization Based on a Large‐Eddy Simulation and Its Impact on Prediction of Hurricane Landfall

The vertical eddy diffusivity (VED) in the planetary boundary layer (PBL) affects tropical cyclones' structure and evolution. Uncertainties of VED in the PBL parametrization scheme of a mesoscale model could be caused by the model's inability to represent large eddies (LEs). Using a large‐eddy simulation (LES) of Hurricane Harvey (2017) as a benchmark, the YSU PBL scheme is improved by adding effects of LEs derived from the LES. It is found that LEs' maximum intensity is linearly significantly related to the square of mean horizontal divergence below 400 m of height at the same air column with a slope coefficient of 1.97. The revised YSU scheme relates the VED of momentum (Km) to the square root of LEs' intensity with a slope coefficient of 0.08 in PBL and 0.20 in a free atmosphere. Compared to the original scheme, the modified YSU scheme leads to improved forecasts of landfalling hurricanes. The turbulent transport in the boundary layer, the low part of the atmosphere near the Earth's surface, affects tropical cyclones' structure and evolution. Its effects are represented by the vertical eddy diffusivity (VED) in the planetary boundary layer (PBL) parameterization scheme of a mesoscale model. Due to the coarser grid spacing of the mesoscale model, the effects of large eddies in the boundary layer cannot be resolved. In this study, a large‐eddy simulation (LES) of Hurricane Harvey (2017) is used as a benchmark to relate the effects of large eddies to the VED of momentum. The derived relationship is then applied to improve a popular PBL parameterization scheme, which has been widely used in the mesoscale models. It is found that compared to the original scheme, the modified YSU scheme leads to improved forecasts of landfalling hurricanes. Large eddies LE)s' maximum intensity is linearly related to the square of mean horizontal divergence below 400 mThe revised YSU scheme relates the vertical eddy diffusivity of momentum to the square root of the LEs' intensityThe modified YSU scheme leads to improved forecasts of landfalling hurricanes Large eddies LE)s' maximum intensity is linearly related to the square of mean horizontal divergence below 400 m The revised YSU scheme relates the vertical eddy diffusivity of momentum to the square root of the LEs' intensity The modified YSU scheme leads to improved forecasts of landfalling hurricanes