DUAL-POLARIZATION RADAR TO IDENTIFY DRIZZLE, WITH APPLICATIONS TO AIRCRAFT ICING AVOIDANCE

Freezing drizzle has been identified as a primary aircraft in-flight i cing hazard. New evidence shows that it can be a greater hazard than f reezing rain, even though the latter can be significant. Freezing driz zle may form by droplet coalescence without an intermediate melting pr ocess, so that it also can be more difficult to detect than freezing r ain. Theoretical calculations of microwave scattering and verification by the initial field studies presented here demonstrate that freezing drizzle should be detectable and distinguishable from other hydromete or types in short-wavelength, dual-polarization radar measurements of elliptical and linear depolarization ratios. A practical procedure is suggested for identifying and monitoring this aviation hazard with the radar and concurrent atmospheric temperature measurements. The WSR-88 D radar (NEXRAD) has the potential to add dual-linear polarization to operationally apply this method, within certain constraints.