Retrieval of atmospheric liquid and ice characteristics using dual-wavelength radar observations

Dual-wavelength (K/sub /spl alpha//- and X-band) radar measurements have shown promise in estimating the amount of liquid water in a cloud. By taking advantage of the attenuation by liquid water of the K/sub /spl alpha//-band signal as compared to X-band, the range-differentiated difference in reflectivity can be used to estimate the spatial distribution of cloud liquid water. One limitation is that the method is based on the assumption that all particles in the radar beams act as Rayleigh scatterers, that is, their diameters are small compared to the radar wavelengths. In natural clouds in wintertime conditions, this often may not be the case. This paper presents simulations of the response of these two wavelengths to conditions measured in several geographic locations. The simulations are used to build simplified relations between radar reflectivity and total mass and size distribution functions of liquid droplets and ice particles. Using these relations, it may be possible to estimate the sizes of the droplets, as well as total mass contents and size distributions of ice particles that may also be present in the sampled volume. Results of radar-based retrieval methods applied to measurements in a winter stratiform cloud are discussed, and compared with a previous result. A technique is described for detecting regions of non-Rayleigh scattering and for subsequently estimating liquid water content (LWC). Additional examples of dual-wavelength measurements in regions containing cloud droplets, small ice particles, and larger snowflakes are discussed.