2 Capturing the Nocturnal Boundary Layer Processes at Cabauw

Monday, 20 June 2016
Alta-Deer Valley (Sheraton Salt Lake City Hotel)
S.J.A. van der Linden, Delft University of Technology, Delft, Netherlands; and P. Baas and B. J. H. Van de Wiel

In many idealised, numerical studies of the nocturnal boundary layer, using e.g. LES or DNS, a type of simplified surface boundary conditions is used. Examples are the use of a constant surface heat flux or a prescribed surface temperature. In reality, however, the atmosphere and the surface form a coupled system in which heat can be exchanged. Operational models on the other hand do use realistic surface couplings, but are less suitable for theoretical analysis due to their complexity.

Here, we opt for a model of intermediate complexity which allows in depth analysis of the stable boundary layer with coupling to vegetation and soil through a surface energy budget. The model is used to investigate the nonlinear feedbacks between the flow and the ground. By benchmarking to selected ensemble observations from the Cabauw site in the Netherlands, we aim to capture the basic 10-year climatology of the site for varying wind speed classes.

The goal is to find critical dimensionless parameters to predict the transition from the weakly stable to the very stable case. We expect that in addition to mechanical forcing, unknown parameters involving ground properties, will play a role in critical flow transitions.

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