14th Conference on Mountain Meteorology


The angle of near-surface wind-turning in weakly stable boundary layers

Branko Grisogono, Department of Geophysics, Faculty of Science, Zagreb, Croatia; and L. Enger

The angle between the near-surface and geostrophic wind vector is discussed in the light of existing and improved Ekman theory and, on the other hand, recently obtained numerical results corroborated by some experimental data, both obtained by other researchers. The latter results for weakly stable boundary layers, also based on LES data, show that this angle is about alpha =~ 35 deg. If the Ekman theory is applied slightly above the horizontal surface for almost any gradually varying eddy diffusivity K(z), which must be a more realistic case than that with K = const used at z = 0 in the classic theory, a closer analytic value to the angle can be provided, i.e. alpha = 32 deg, than that in the classic Ekman theory (45 deg). Alternatively, and without deploying the refined Ekman surface layer theory already suggested here, one may a priori use the previously confirmed result, alpha =~ 35 deg, together with any smooth K(z) in order to find the corresponding surface layer depth. These results, bridging the gap between the existing theory toward fine numerical and limited experimental data, may aid in further analysis of weakly stable boundary layers. The information about the angle alpha should be considered in NWP, air-pollution, wind-energy and climate models; otherwise, many important boundary-layer features will remain modeled inadequately.

wrf recordingRecorded presentation

Session 4, Boundary Layers and Turbulence in Complex Terrain
Monday, 30 August 2010, 3:30 PM-5:15 PM, Alpine Ballroom A

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