237 Identifying Polarimetric Radar Signatures Aloft Associated with Large and Giant Hail

Thursday, 31 August 2017
Zurich DEFG (Swissotel Chicago)
Jeffrey C. Snyder, NOAA/OAR/NSSL, Norman, OK; and A. V. Ryzhkov and J. Krause

Handout (5.9 MB)

The Hail Size Discrimination Algorithm (HSDA), soon to be added to the operational hydrometeor classification algorithm (HCA), attempts to identify large (i.e., equivolume diameter D of at least 2.5 cm) and giant (i.e., D of at least 5.0 cm) hail on a bin-by-bin basis using beam height, reflectivity (ZH), differential reflectivity (ZDR), and co-polar correlation coefficient (ρhv) information at each bin. Although the HSDA has shown skill at identifying regions of large and/or giant hail, it tends to be very sensitive to ZDR miscalibration, and it tends not to identify hail where ZH is relatively low (such as areas near the updrafts of strong supercells, where intense size sorting may produce extremely low number concentrations of giant hail). In an attempt to provide additional lead time and to identify where large and giant hail may be occurring in sparse enough quantities to be associated with modest ZH, we instead turn our attention to signatures and radar characteristics aloft (e.g., 4-10 + km above ground level) for indications that such hail is growing. For example, areas of significantly reduced ρhv (e.g., ρhv < 0.8) and strongly negative ZDR (e.g., ZDR of -1 to -2 dB) have been observed near and above ZDR columns within the mid-levels of giant-hail-producing supercells at least a couple of volume scans before large and giant hail is observed nearer the ground. Using polarimetric radar data from the operational WSR88D network, we examine the potential utility of such polarimetric signatures aloft for enhancing our ability to anticipate and detect large and giant hail within severe convective storms.
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