Comparison of Eddy Dissipation Rates from Spatial Spectra of Doppler Velocities and Doppler Spectrum Widths

Abstract

Doppler radars offer unique data from which it is possible to estimate the turbulent eddy dissipation rates, ?. If the inertial subrange extends to lengths longer than the radar resolution volume size, ? can be obtained from the Doppler spectrum width. Spatial spectra of mean Doppler velocities can also yield ? estimates but only if a significant portion of the analysis length is contained within the inertial subrange. We compare dissipation rate estimates obtained with the two independent measurement techniques. At close range and vertical incidence, agreement between the two independent estimates of ? is within 10%. Furthermore, the slope of the spatial energy densities is very close to ?5/3 predicted by Kolmogorov. The energy input is mainly from buoyancy-driven updrafts and the transition wavelength (about 3 km) between the input scale and the inertial subrange is consistent with the updraft-downdraft circulation cell, which is about 10 km. For a more distant storm at a range of 60 km, the filtering of mean velocities by the resolution volume precludes precise estimation of ? from spatial spectra of mean velocities.