X-band polarimetric and Ka-band Doppler spectral radar observations of a graupel-producing arctic mixed-phase cloud

Characteristics of graupel in an Arctic deep mixed-phase cloud on 7 December 2013 were identified with observations from an X-band scanning polarimetric radar and a Ka-band zenith-pointing radar in conjunction with scattering calculations. The cloud system produced generating cells and strongly sheared precipitation fall streaks. The X-band radar hemispheric RHI observables revealed spatial sorting of polarimetric signatures: decreasing (with increasing range) differential propagation phase shift ϕ_DP, negative specific differential phase KDP collocated with negative differential reflectivity Z_DR in the upper half of the fall streak, and increasing or near-constant ϕ_DP with positive Z_DR at the bottom edge of the fall streak. The negative K_DP and Z_DR, indicating prolate particles with vertically oriented maximum dimensions, were consistent with small, slow-falling conical graupel coexisting with low concentrations of more isometric graupel. The observed negative K_DP values were best matched by scattering calculations for small, dense conical graupel with 30°-40° cone angles. The positive K_DP and Z_DR and the Doppler spectra indicate that large isometric graupel coexisted with a second population of slower-falling rimed platelike particles in the lower half of the fall streak. Through the core of the fall streak, ϕ_DP decreased in range while Z_DR was slightly positive, indicating that the prolate conical graupel dominated ϕ_DP while the isometric larger graupel dominated reflectivity (and thus Z_DR). These results demonstrate the capability of polarimetric observables and Doppler spectra to distinguish different growth stages of rimed particles, allowing for the improvement of hydrometeor classification methods.