Assessing the Errors of Microphysical Retrievals Based on Doppler Radar Parameters

The paper analyzes errors in retrievals of cloud liquid water content (Ql) and precipitation flux (R) based on three different sets of parameters: a) radar reflectivity, Z, b) radar reflectivity and Doppler velocity, V , and c) radar reflectivity and Doppler velocity spectrum width, σ d d. As radar reflectivity represents the sixth moment of the drop size distribution (DSD), one can expect it to be correlated with other moments of the DSD, such as liquid water content Ql (third moment of DSD), or drizzle flux R, which in stratocumulus clouds is proportional to the fourth DSD moment. Thus, a number of studies have been devoted to retrievals of Ql and R in boundary layer stratocumulus based on radar reflectivity Z alone. The success of the Ql retrievals depended on cloud type, but even more on the absence of drizzle, both in the cloud and below cloud base. The retrieval of Ql is rather straightforward in non-drizzling stratocumulus where cloud spectra are mostly unimodal and the contribution to reflectivity from the large droplet tail of the spectrum is minimal. A simple Z-Q relation in this case is justified (Sauvageot and Omar 1987; Frisch et al. 1995; Fox and Illingworth 1997):