P. (Peter) Baas: “Turbulence and Low-Level Jets in the Stable Boundary Layer”

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14 Oct 2009 16:00
Unit: Wageningen University
Location: Aula, building 362, Gen. Foulkesweg 1, Wageningen
Organisation: Wageningen University
Promotor: prof.dr. B. Holtslag (Meteorology and Air Quality)
Co Promotor: Dr. F.C. Bosveld (KNMI, De Bilt)

 It is common knowledge that in the evening the wind close to the ground drops. However, it is less well known that at the same time the wind at a few hundreds of meters height can strongly accelerate. In this case, the vertical wind-profile shows a distinct maximum. This phenomenon is called nocturnal low-level jet (LLJ). Knowledge of the LLJ is relevant for aviation, the generation of wind energy and the distribution of pollutants. This thesis presents a climatology of LLJ characteristics (like the frequency of occurrence and the typical height at which the phenomenon occurs) for observations from the KNMI measurement site at Cabauw.

The development of nocturnal LLJs is very sensitive to the amount of turbulent mixing. In this thesis different ways on which turbulence is represented in atmospheric models are tested. Various strategies for model evaluation are discussed. This thesis aims to contribute to the understanding of physical processes and their representation in weather and climate models.
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