Modeling and Interpretation of S-Band Ice Crystal Depolarization Signatures from Data Obtained by Simultaneously Transmitting Horizontally and Vertically Polarized Fields

Data collected by the National Center for Atmospheric Research S-band polarimetric radar (S-Pol) during the Terrain-Influenced Monsoon Rainfall Experiment (TiMREX) in Taiwan are analyzed and used to infer storm microphysics in the ice phase of convective storms. Both simultaneous horizontal (H) and vertical (V) (SHV) transmit polarization data and fast-alternating H and V (FHV) transmit polarization data are used in the analysis. The SHVZ dr(differential reflectivity) data show radial stripes of biased data in the ice phase that are likely caused by aligned and canted ice crystals. Similar radial streaks in the linear depolarization ratio (LDR) are presented that are also biased by the same mechanism. Dual-Doppler synthesis and sounding data characterize the storm environment and support the inferences concerning the ice particle types. Small convective cells were observed to have both large positive and large negativeK dp(specific differential phase) values. NegativeK dpregions suggest that ice crystals are vertically aligned by electric fields. Since high |K dp| values of 0.8° km−1in both negative and positiveK dpregions in the ice phase are accompanied byZ drvalues close to 0 dB, it is inferred that there are two types of ice crystals present: 1) smaller aligned ice crystals that cause theK dpsignatures and 2) larger aggregates or graupel that cause theZ drsignatures. The inferences are supported with simulated ice particle scattering calculations. A radar scattering model is used to explain the anomalous radial streaks in SHVZ drand LDR.