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.