Doppler Radar Observations of Momentum Flux in a Cloudless Convective Layer With Rolls

Dual Doppler radars are used to obtain momentum flux and turbulence intensities in the cloudless convective boundary layer (CBL) containing roll vortices. Momentum flux for small scales unresolved by the radar is determined from the difference between the measured flux and the flux implied by the velocity defect profile. While the small-scale flux indicates a reasonable eddy diffusivity profile, the measured flux is of the opposite sign expected from K theory. Two terms in the turbulent kinetic energy budget--the shear production and the divergence of the energy flux--are calculated for measurable scales. It is proposed that the tilting of convective roll circulations by cross-shear produces the observed flux in the upper part of the CBL.