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X-Band Polarimetric and Ka-Band Doppler Spectral Radar Observations of a Graupel-Producing Arctic Mixed-Phase Cloud

2015; American Meteorological Society; Volume: 54; Issue: 6 Linguagem: Inglês

10.1175/jamc-d-14-0315.1

1558-8432

Mariko Oue, Matthew R. Kumjian, Yinghui Lu, Zhiyuan Jiang, Eugene E. Clothiaux, Johannes Verlinde, Kültegin Aydin,

Aeolian processes and effects

Abstract 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 K DP 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.