Time Evolution and Diurnal Variability of The Parametric Sensitivity of Turbine‐height Winds In The Mynn‐edmf Parameterization

Abstract

The Mellor‐Yamada‐Nakanishi‐Niino (MYNN) parameterization applied in the Weather Research and Forecasting (WRF) model has been augmented to include the Eddy‐Diffusion Mass‐Flux (EDMF) approach to better represent transport by boundary‐layer eddies. This change includes the addition of new parameters associated with convective updrafts and boundary‐layer clouds that lead to new parametric sensitivities in the turbine‐height wind speed compared to simulations using the standard MYNN parameterization. This work builds on efforts focused on WRF’s MYNN parameterization by examining the sensitivity of wind speed to parameters in the MYNN‐EDMF parameterization as a function of simulation duration. Summer and winter periods were selected from the second Wind Forecast Improvement Project (WFIP2). Five sets of simulations were completed for each season, with durations ranging from 2 to 6 days. The results show that the sensitivity to the new parameters associated with the EDMF scheme is generally small compared to other parameters in clear conditions, but the sensitivity to the entrainment becomes significant when the updraft fraction is large. The spread in the perturbed parameter ensembles was found to grow quickly over the first 8 to 19 hours in the summer simulations and 17 to 24 hours in the winter simulations with little change after that, regardless of the simulation length. A strong diurnal cycle in the parameter sensitivity was also found associated with the atmospheric stability, as well as an increase in the sensitivity to the entrainment parameter used in the EDMF parameterization that is associated with increasing fractional area covered by plumes.