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

126127128129130131132133134135136137138139140141142143144145146147algorithm definitions and equations). The T-matrix model computes the radar backscatteringcross section of particular hydrometeors and the Mueller-matrix calculates polarimetric radarobservations for a homogeneous, parameterized population of a given hydrometeor type. Theseresults are sensitive to the input parameters in Table 1, which we elaborate on in the remainder ofthis section.All hydrometeors are modeled as oblate spheroids without branched or otherwiseirregular shapes, which is sufficient for X-, C-, and S-band weather radar applications (Bringiand Chandrasekar 2001). While scattering simulations are sensitive to phase (ice vs. liquid), theresults were negligibly sensitive to changes in temperature. 30° and 1° elevation angles weresimulated to determine how the radar would perceive high- and low-altitude ice particles. Sleetand rain are only expected to exist below the melting level so are simply modeled at 1°.Hydrometeor bulk density (! bulk ) is defined as the particle’s mass per unit volume. Theaxis ratio is assumed to compare the minor (“a”, basal, a-axis growth face) and major (“b”,prism, c-axis face) dimensions of a particle (“a/b”), where values approach one for spheres. Theparticle size distribution (PSD) D MIN , D MAX , diameter interval ("D), and functional shape areparameterized, from which we calculate D 0 . To represent the natural variability of precipitationin turbulent background flow, all hydrometeors are assumed to have a Gaussian distribution ofcanting angles about a mean (# m ) of zero (Beard and Jameson 1983, Hendry et al. 1976, Spek etal. 2008). The fall behavior of individual particles may vary greatly, but in the interest ofdistinguishing bulk hydrometeor types we used standard deviation of the canting angle ($) valueswhich best characterized how each particle type might fall differently from another.b) Model parameterizations for various hydrometeors7