On the unified estimation of turbulence eddy dissipation rate using Doppler cloud radars and lidars

Coincident profiling observations from Doppler lidars and radars are used to estimate the turbulence energy dissipation rate (epsilon) using three different data sources: (i) Doppler radar velocity (DRV), (ii) Doppler lidar velocity (DLV), and (iii) Doppler radar spectrum width (DRW) measurements. The agreement between the derived epsilon estimates is examined at the cloud base height of stratiform warm clouds. Collocated epsilon estimates based on power spectra analysis of DRV and DLV measurements show good agreement (correlation coefficient of 0.86 and 0.78 for both cases analyzed here) during both drizzling and nondrizzling conditions. This suggests that unified (below and above cloud base) time-height estimates of epsilon in cloud-topped boundary layer conditions can be produced. This also suggests that eddy dissipation rate can be estimated throughout the cloud layer without the constraint that clouds need to be nonprecipitating. Eddy dissipation rate estimates based on DRW measurements compare well with the estimates based on Doppler velocity but their performance deteriorates as precipitation size particles are introduced in the radar volume and broaden the DRW values. Based on this finding, a methodology to estimate the Doppler spectra broadening due to the spread of the drop size distribution is presented. The uncertainties in epsilon introduced by signal-to-noise conditions, the estimation of the horizontal wind, the selection of the averaging time window, and the presence of precipitation are discussed in detail.