Polarimetric Radar Signatures of Hydrometeors Observed within Mature Convective Storms

Polarimetric radar has the ability to distinguish shape, size, and orientation of hydrometeors in the atmosphere. Inferences can therefore be made from the polarimetric variables, through the use of hydrometeor classification algorithms, about the radar-dominant hydrometeor species within a given radar volume. These radar observations are typically made far above the earth's surface, and verifying the hydrometeor type corresponding to a given set of polarimetric variables consequently presents challenges.

To address this issue, in situ measurements were obtained from within thunderstorms by a suite of hydrometeor probes on the armored T-28 aircraft. The hydrometeor observations were compared with concurrent radar data from both the prototype dual-polarimetric WSR-88D in Norman, Oklahoma (KOUN) as well as the CSU-CHILL dual-polarimetric radar. Radar volumes co-located with the position of the penetrating T-28 aircraft were found, and polarimetric variables from these volumes were extracted and compared with the hydrometeor images from the various T-28 imaging probes. The purpose was to identify the polarimetric radar signatures of the observed hydrometeor types.

Results illustrate some distinct relationships between differing hydrometeor types and their corresponding polarimetric variables. Moreover, when particular pairs of polarimetric variables are plotted against each other (e.g., Z vs. ρ_hv) in two-dimensional space with respect to the differing hydrometeor types, the distinctions are better seen. Ranges of the polarimetric variables are discussed in the context of membership functions associated with the current automated hydrometeor classification algorithms of Liu and Chandrasekar (2000) and Park et al. (2009). Some suggestions are made for improving these algorithms and membership functions on the basis of the in situ observations.