Spectral Characteristics of the Convective Boundary Layer Over Uneven Terrain

Abstract

The paper describes a convective boundary layer experiment conducted in April 1978 at the Boulder Atmospheric Observatory, and examines the spectral behavior of wind velocity and temperature from the Observatory's 300 m tower, from aircraft flights alongside the tower and from a surface network of anemometers, for evidence of terrain influence on turbulence structure. The gently rolling terrain at the site does not seem to affect the turbulence spectra from the tower in any perceptible manner, except for minor shifts in the vertical velocity and temperature spectral peaks. The aircraft vertical velocity spectra showed different shapes for alongwind and crosswind sampling directions, as in earlier measurements over ocean surfaces, and their peaks are displaced to higher wavenumbers compared with the tower spectra. Long-term spectra of horizontal wind components from surface stations around the tower exhibit no particular sensitivity to site selection. Under near-stationary conditions the peak of the spectrum of the streamwise component tends to reflect more closely the predominant boundary layer. convective scales than does the peak of the lateral wind component. The problem of identifying those scales in the presence of large shifts in wind direction is discussed.