1. Evidence of strong wave turbulence and of Bolgiano temperature spectra in katabatic winds on steep slopes.
- Author
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Charrondière, C., Hopfinger, E. J., Brun, C., Cohard, J.-M., and Sicart, J.-E.
- Subjects
KATABATIC winds ,REYNOLDS number ,TURBULENCE ,WIND speed ,POWER spectra ,WAVE energy - Abstract
The katabatic winds on steep slopes investigated in the present study reveal a novel spectral behavior, observed in the outer part of the jet. At low wavenumbers, the one-dimensional (1D) velocity spectra show evidence of a k x − 1 range for the three components of the velocity vector: E u (k x) , E v (k x) , E w (k x) ∝ k x − 1 [as well as for the 1D temperature spectrum E θ (k x) ∝ k x − 1 ]. This suggests the existence of strong wave turbulence. A necessary condition for strong wave turbulence to be manifest is that the flow direction wavenumber, k
x , extends to much lower values than the slope normal one, kz . This is satisfied in the present field experiment where wave energy is injected at wavenumber k x = k N = (N a sin α) / u j ¯ , while k z ∼ 1 / Δ z , with Na the ambient stratification, α the slope angle, u j ¯ the maximum wind velocity, and Δ z the shear layer thickness of the jet. In the inertial range, the velocity spectra exhibit a power law k x − 5 / 3 over two decades, whereas the temperature-buoyancy spectra show evidence of a − 7 / 5 slope in the buoyancy sub-range, followed by a − 5 / 3 slope. The change in spectral slopes occurs at the Bolgiano scale LB that is close to the Dougherty–Ozmidov scale LOZ . The high Reynolds number based on the Taylor micro-scale, R e λ ∼ 10 3 , allows clear identification of the spectral laws. [ABSTRACT FROM AUTHOR]- Published
- 2024
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