Simulation of the observed evening transition and nocturnal boundary layers: Single‐column modelling

Observations of the evolution of the atmospheric boundary layer through the evening transition and the early hours of the night are presented. Parallel simulations in a single‐column model are conducted to assess the performance of the parametrization scheme and the sensitivity to vertical resolution. The study is set within the context of a numerical weather‐prediction system and the importance of the synoptic situation is emphasized. Comparisons are also drawn with an accompanying study describing large‐eddy simulations based on these same data. These show that, when the single‐column model is run with sharp‐tailed stability functions, turbulent diffusion is systematically underestimated in and just above the surface layer, while it is overestimated at greater heights; the parametrized profile of diffusivity is therefore too uniform, causing the temperature profile in the single‐column model to exhibit negative curvature, rather than the positive curvature seen in the observations and in the large‐eddy simulations.