Mixed-Phase Cloud Retrievals Using Doppler Radar Spectra

The radar Doppler spectrum contains a wealth of information on cloud microphysical properties. Typically, radar-based cloud retrievals use only the zeroth or first moments of the Doppler spectrum – reflectivity and mean Doppler velocity – to derive quantities such as cloud water content and particle characteristic size (e.g., Liou and Sassen 1994; Matrosov et al. 2002). When using only the moments of the Doppler spectrum, important spectral information can be lost, particularly when the spectrum is multi-modal. Multi-modal spectra are possible when a mixture of two or more cloud particle phases, habits, or sizes exist in the same volume (e.g., Gossard et al. 1997). For example, the large difference in size between the liquid droplets and ice crystals in a mixed-phase cloud often causes these two phases to fall at different rates, thus producing a bi-modal spectral signature.