Simulation of the observed evening transition and nocturnal boundary layers: Large-eddy simulation

Large-eddy simulations are performed of two observed cases of evening transition boundary layers over land. Although generally similar to the observations, the simulations have a poor match to the ageostrophic wind above the boundary layer and overestimate the nocturnal 4 m wind speed. For one case, the nocturnal phase is also simulated using a close match to observations in the early evening, reproducing well the early morning boundary layer and jet. This is achieved with a moderate resolution (5 m) and also demonstrates the importance of a good initial wind state. In a numerical weather-prediction context, these findings motivate improved wind profile observations around transition, and a better representation of the ageostrophic wind by the boundary-layer parametrization.