2005: Turbulence measurements in marine stratocumulus with airborne Doppler

This study investigates the ability of a W-band radar to measure turbulence structure as a function of height throughout the drizzling marine boundary layer from the ¯ne-structure of the Doppler velocity ¯eld. In situ air velocity measurements are used as a basis for the comparison with radar measurements of turbulence energy and dissipation, and integral length scale, after correcting for the e®ects of velocity averaging within the pulse resolution volume and random uncorrelated noise. One essential step for this study is to estimate the contribution to the °uctuations in Doppler velocity due to the terminal velocity of hydrometeors. To do this, we use microphysics probe measurements of the spatial distribution of the drop counts in each size bin. We ¯nd a small Doppler velocity standard deviation (0.05 to 0.1 m s¡1) due to drop fall velocity and a substantial negative correlation between air vertical velocity and Doppler fall velocity in the upper part of the cloud. This correlation has an impact on the turbulent energy and dissipation deduced from the Doppler velocity. However, it does not signi¯cantly a®ect the integral scales, which are in good agreement with the in situ measurements. Thus, the radar enables us to obtain the pro¯le of this key variable through the entire cloud-capped boundary layer. We obtain estimates of the dissipation in the lower 2/3 of the boundary layer that are in excellent agreement with the in situ measurements and consistent with the predominant production terms in the turbulent kinetic energy budget