UBC Theses and Dissertations
Spectral analysis of turbulence in an unstable suburban atmosphere Roth, Matthias
To measure variances and covariances of meteorological variables over very rough surfaces such as tall crops, forests and urbanized areas, that are consistent with Monin-Obukhov similarity theory, it is essential to avoid the roughness sub-layer, where the fluxes are affected by wake effects introduced by individual roughness elements. It is also necessary to work in the surface layer where height above the effective surface is the only length scale and the semi-logarithmic profile laws are obeyed. This thesis provides turbulence spectra of temperature, the vertical and longitudinal wind components as well as the fluxes of sensible heat and momentum measured in an unstable surface layer over a suburban surface. The sensor height employed in the field programme is at or below recommended values for the top of the roughness sub-layer, hence there is reason to question whether the observations are influenced by wake effects. This is of importance since the same measurement height has been used in computations of turbulent fluxes for energy balance studies at this site. The (co)spectra, normalized with the (co)variances, for all quantities investigated show very good agreement with reference data from smoother surfaces and the few studies available from other urban turbulence programmes. This study provides the first composite cospectra of sensible heat and momentum over urban terrain. It is concluded that the site used is suitable in regard to turbulence and energy balance measurements representing suburban terrain. An ancillary result shows that the recommended averaging times for the turbulent fluxes can be relaxed.
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