Closely Spaced X-band Dual-Wavelength Dual-Polarization Signatures in Melting Hail

Traditional dual-frequency weather radar techniques employ two widely spaced frequency bands, selected such that one produces scattering that can be described by the Rayleigh approximation, and one for which hydrometeors are large compared to the wavelength. Recent studies, however, have suggested that closely spaced frequencies within the same band may produce a differential response in large hydrometeors (i.e., those that cause resonance scattering effects), based on observations from two different radars. The recent upgrade of the Doppler on Wheels (DOW) radars to dual-polarization with dual-X-band frequencies (DOW7: 9.5 GHz and 9.35 GHz, DOW6: 9.55 and 9.40 GHz) using the same antennas allows us to explore the possibilities of hail detection and/or sizing using matched beams.

Data were obtained from a storm that produced hail up to the size of dimes during the DOW7 visit to Penn State in late 2014. High-resolution RHI scans through the storm reveal dual-frequency differences in the polarimetric radar variables. T-matrix scattering calculations reveal that the observations are consistent with resonance scattering by wet hail within narrow size bands. Additional dual-frequency differences are consistent with wavelength-dependent propagation effects (or artifacts) such as differential attenuation, depolarization, and nonuniform beam filling. The implications of these observations for hail detection and sizing and for validating theoretical models of propagation effects will be discussed. The results suggest hail sizing within narrow bands is possible for closely spaced radar frequencies.