1 A dual-polarization radar hydrometeor classification algorithm for ...

329330331332333334335336337338339340341342343344345346347348349350351Modifications to this algorithm necessitated (a) new procedures, (b) new membership betafunctions, and (c) a variable weighting system for each precipitation category. These three stepssubstantially increased the algorithm’s ability to distinguish different precipitation categoriesaccording to literature examples of these features, decreased its reliance on external temperaturedata to make classifications, and allowed it to work well on a variety of radar platforms.This algorithm assumes ice or mixed-phase precipitation is occurring somewhere in thedomain so an appropriate convective warm-season algorithm should be consulted under otherconditions. Non-meteorological echo must be removed a priori. A 5 dBZ reflectivity and 7-10 dBSNR threshold was also used to avoid misclassifications at echo edges due to nonmeteorologicalZ dr increases.a) Algorithm proceduresAs is typical for many HCAs, classification is performed on each pixel without knowledge ofdecisions made for nearby pixels or how the radar variables trend with height and time. Park etal. (2009) suggests that HCA performance can be optimized if individual algorithms aredeveloped for each major precipitation regime. It may be unrealistic to design a single algorithm(or single set of MBFs) to handle convective, stratiform, warm, and cold-season precipitation.Our HCA methodology is demonstrated during a stratiform freezing rain event in centralOklahoma with the C-band OU-PRIME radar in Norman, OK (Palmer et al. 2011). The nearbysoundings for this event are shown in Fig. 3, which exhibit a strong temperature inversion and acold surface layer from 15 UTC until 21 UTC. Fig. 4 shows the 2.4° PPI of OU-PRIME C-bandpolarimetric radar variables through the melting layer of stratiform precipitation when METARreports indicated freezing rain at the surface. A DGZ of enhanced K dp and Z dr with reduced ! hvappears aloft toward the southwest. This particular radar scan was used to verify that the16