Turbulence spectra and dissipation rates in a wind tunnel model of the atmospheric convective boundary layer

A model of the atmospheric convective boundary layer (CBL) is realized in the thermally stratified wind tunnel of the Institute of Hydrology and Water Resources, University of Karlsruhe. Further experimental results from this model are presented. The wind tunnel with a test section 10 m long, 1.5 m wide, and 1.5 m high allows one to generate a quasi-stationary, horizontally evolving CBL, characterized by convective Richardson numbers RiDT up to 10 and RiN up to 20, with the bottom shear/buoyancy dynamic ratio u /w in the range of 0.2 to 0.5. The convective regime in the tunnel is dominated by bottom-up forcings. Effects of entrainment in the simulated CBL play a secondary role. The spectra of turbulence in the wind tunnel flow are calculated from high-resolution velocity component and temperature time series, simultaneously measured using laser Doppler and resistance-wire technique, respectively. The spectra from the mixed core of the CBL and in the entrainment zone display pronounced inertial subranges. The ratio of vertical to horizontal velocity spectra in these subranges is within the interval from 1.3 to 2, which is slightly larger than could be expected for purely isotropic turbulence. Different maxima in the productio