Similarity Scaling Over a Steep Alpine Slope

Daniel F. Nadeau, Eric R. Pardyjak, Chad W. Higgins, Marc B. Parlange

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40 Citations (Scopus)

Abstract

In this study, we investigate the validity of similarity scaling over a steep mountain slope (30-41°). The results are based on eddy-covariance data collected during the Slope Experiment near La Fouly (SELF-2010); a field campaign conducted in a narrow valley of the Swiss Alps during summer 2010. The turbulent fluxes of heat and momentum are found to vary significantly with height in the first few metres above the inclined surface. These variations exceed by an order of magnitude the well-accepted maximum 10 % required for the applicability of Monin-Obukhov similarity theory in the surface layer. This could be due to a surface layer that is too thin to be detected or to the presence of advective fluxes. It is shown that local scaling can be a useful tool in these cases when surface-layer theory breaks down. Under convective conditions and after removing the effects of self-correlation, the normalized standard deviations of slope-normal wind velocity, temperature and humidity scale relatively well with z/Λ, where z is the measurement height and Λ (z) the local Obukhov length. However, the horizontal velocity fluctuations are not correlated with z/Λ under all stability regimes. The non-dimensional gradients of wind velocity and temperature are also investigated. For those, the local scaling appears inappropriate, particularly at night when shallow drainage flows prevail and lead to negative wind-speed gradients close to the surface.

Original languageEnglish
Pages (from-to)401-419
Number of pages19
JournalBoundary-Layer Meteorology
Volume147
Issue number3
DOIs
Publication statusPublished - Jun 2013
Externally publishedYes

Keywords

  • Downslope flow
  • Drainage flow
  • Flux divergence
  • Flux-gradient relationships
  • Flux-variance relationships
  • Local similarity
  • Mountain winds
  • Surface layer

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