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

306307308309310311312313314315316317318319320321322323324325326327328in Fig. 1 and the rest of this study) as opposed to the small oscillations consistent with liquidraindrops deforming as they fall, the additional decrease in Z h is nearly zero but there is a 25%further decrease in both K dp and Z dr . While it is obvious that these three radar variables shoulddecrease once rain has completely frozen, these findings show that the dielectric factor anddensity decrease from liquid to ice dominates these trends, canting has a secondary, nonnegligibleeffect, and temperature has little importance.More importantly, since Figs.1 and 2 show how radar variables associated with stratiformrain encompass that of both supercooled and frozen rain, these latter two phenomena couldsimply be attributed to light rain. If the expected value ranges of a hydrometeor type are notunique from another type, fuzzy logic HCA MBFs cannot distinguish them. This simplealgorithm also cannot accommodate detection of the localized, small magnitude refreezingsignature associated with the production of sleet because those expected value ranges also liewithin that of stratiform rain (Kumjian et al. 2013). These include an increase in Z dr and K dpalong with decreased ! hv and Z H . If 2-D MBFs (Zrnic et al. 2001) and/or texture fields (Ryzkovet al. 2005b) were incorporated into the decision process, the spatial, correlated variability in ! hv,Z dr, K dp, and Z h within the refreezing signature might prompt more accurate rain/freezingrain/sleet classification. In the meantime, our methodology relies primarily on temperature toclassify rain and the combined possibility of sleet and/or freezing rain below the melting layerwhere T < 0 C without assessing other possible thermodynamic factors as in Schuur et al. (2012).4. Algorithm development and testingThe fuzzy-logic hydrometeor classification algorithm described in DR09 was adapted forwinter precipitation types to include stratiform rain, freezing/frozen raindrops (i.e., sleet and/orfreezing rain), wet snow (indicative of the melting layer), aggregates, dendrites, and plates.15