Improving the Mellor–Yamada–Janjić Parameterization for wind conditions in the marine planetary boundary layer

Abstract

Listen

Translate article

The structure of the lower part of the marine planetary boundary-layer (PBL) is relevant not only for climate and numerical weather prediction simulations but also for commercial applications such as offshore wind energy harvesting. A proper description of turbulence might have an important influence on the wind field properties such as the mean wind speed, turbulent fluxes and especially the vertical wind profile. In this study, the Mellor–Yamada–Janjic boundary-layer and surface-layer parameterizations in the Weather Research and Forecasting Model (WRF) were improved by redefining the master length scale (MLS), which controls the diffusion and dissipation of the turbulent fluxes as well as the pressure– temperature and pressure–strain covariances. In the surface layer, the modified MLS is dependent on the surface stability. In the PBL, the surface stability correction of the MLS is included, which has the strongest influence close to the surface. The non-local effects in the stable boundary layer based on surface heat forcing are also included. WRF model simulations with the original and the new PBL parameterization were compared with measurements. Improvements in the wind-shear simulations in the lower part of the boundary layer (up to around 30 m) with the new parameterization have been found, while its impact higher in the PBL is less pronounced. The simulated wind speed is however only slightly dependent on the boundary layer parameterization.