Turbulence spectra in the near-neutral surface layer over the Loess Plateau in China
- 153 Downloads
We present the power spectra of wind velocity and the cospectra of momentum and heat fluxes observed for different wind directions over flat terrain and a large valley on the Loess Plateau. The power spectra of longitudinal (u) and lateral (v) wind speeds satisfy the −5/3 power law in the inertial subrange, but do not vary as observed in previous studies within the low frequency range. The u spectrum measured at 32 m height for flow from the valley shows a power deficit at intermediate frequencies, while the v spectrum at 32 m downwind of the valley reaches another peak in the low frequency range at the same frequency as the u spectrum. The corresponding peak wavelength is consistent with the observed length scale of the convective outer layer at the site. The v spectrum for flat terrain shows a spectral gap at mid frequencies while obeying inner layer scaling in its inertial subrange, suggesting two sources of turbulence in the surface layer. All the spectra and cospectra from the valley direction show a height dependency over the three levels.
KeywordsCospectra Loess Plateau Power spectra Spectral gap Topography
Unable to display preview. Download preview PDF.
- Hunt JCR and Morrison JF (2000). Eddy structure in turbulent boundary layers. Euro J Mech B Fluids 19: 673–694 Google Scholar
- Kaimal JC, Finnigan JJ, (1994) Atmospheric boundary layer flows. Oxford University Press, New York, 289 ppGoogle Scholar
- McNaughton KG, (2004a) New models of the unstable atmospheric surface layer. Proceedings of the 6th International Study Conference on GEWEX in Asia and GAME, Dec, 2004, Kyoto, JapanGoogle Scholar
- McNaughton KG, (2004c) On the budget of turbulence kinetic energy in the unstable atmospheric surface layer. 16 Symp. Boundary Layers & Turbulence, 9–13 July, Portland, Maine, USA. Amer Meteorol Soc Paper 7.7Google Scholar