A Study of the Convective Boundary-Layer Dynamics Using Single Doppler Radar Measurements

Abstract

The kinematic and dynamical properties of the convective planetary boundary layer (CBL) with shear are studied using single Doppler radar measurements. The data were collected using single K-band (0.87 cm) Doppler radar operated by the National Oceanic and Atmospheric Administration Wave Propagation Laboratory. An analysis technique has been developed and tested that is an extension of the velocity azimuth display (VAD). The technique and its associated error analysis are described in detail. Profiles of the mean wind, vertical velocity, associated momentum fluxes, and variances are estimated. In agreement with the classical picture of the CBL, the profile of the vertical velocity variance achieves a relative maximum magnitude in the lower part of the mixed layer. Large magnitudes of vertical flux of horizontal momentum are found at the top of the mixed layer, while countergradient momentum fluxes are found in part of the CBL. The second moment of the Doppler spectrum is utilized, so that the momentum transport by eddies smaller than radar resolution volume is included. In most cases and contrary to most large eddy simulations studies, the effects of the subresolution momentum fluxes on the mixed layer are not negligible. The longitudinal power spectrum of the horizontal velocity near the surface has also been calculated using the Fourier transform techniques. Traditional ??5/3 spectra at the inertial subrange are obtained from which, using standard techniques, the turbulent kinetic energy dissipation rate has been estimated. To test the validity of the single Doppler analysis techniques, the derived turbulence statistics are compared with the results from other measurements.