Precipitation characteristics of supercell hook echoes

Recent studies have suggested that thermodynamic properties of supercell rear-flank downdrafts can affect whether or not tornadogenesis occurs. The thermodynamic characteristics of rear-flank downdrafts are determined in part by microphysical processes such as evaporation of raindrops and melting of hailstones. Whereas in situ measurements of changes in the hook echo particle size distributions (PSDs) due to certain microphysical processes are exceedingly rare, polarimetric radars can be used to determine changes in the characteristics of PSDs remotely.

Analysis of polarimetric radar data from numerous supercell hook echoes reveals unusual drop size distributions compared to typical rainfall in Oklahoma, as well as spatially inhomogeneous structures. For example, the inner edge of the hook echo is often characterized by very high Z_DR, indicative of a sparse population of very large drops. The bottom and/or back portion of the hook is characterized by moderate to high Z_H and rather low Z_DR, indicating a surplus of small drops (or lack of larger drops). Hypotheses explaining the unusual drop size distributions are presented.