Polarimetric radar characteristics of large hail

The advantage of dual-polarization radar data in the discrimination of precipitation types has been demonstrated successfully, including the detection of hail among other precipitation echoes. However, the scattering characteristics of hailstones vary widely across the spectrum of sizes and shapes, and are significantly dependent on the degree of melting and the probing radar wavelength. The most substantial societal impact comes from those hailstones considered severe (> 2.5 cm in diameter) by the National Weather Service, as such large hail inflicts the most damage to property. Therefore, it is necessary to determine any distinct polarimetric or scattering properties of such large hail, which will aid in the detection, discrimination, and warning of severe hail events.

This paper explores the polarimetric radar characteristics of large and giant hail using several approaches, including T-Matrix scattering computations, output from bin microphysics models and the Hebrew University Cloud Model, and observations at both S and C bands. The result is a novel set of rules used to discriminate between large (severe) and small hail, taking into account the height of the hailstones relative to the melting layer. The algorithm was tested on several cases including most recent extreme hail event in Oklahoma City on May 16, 2010 for which extensive ground truth is available.