A Differential Reflectivity Radar Hall Measurement Technique: Observations during the Denver Hailstorm of 13 June 1984

Abstract

A differential reflectivity radar technique for observing hailstorms is demonstrated using measurements obtained during the 13 June 1984 Denver hailstorm. The hail regions of the storm are identified with the differential reflectivity hail signal. Histograms of ZH and ZDR are generated for different heights in the hail regions and the relative variation of these parameters is also determined. It is observed that due to melting, the mean values of ZH and ZDR increase with decreasing height below the 0°C level (which is around 2.6 km above ground level). Furthermore, at the lower levels ZDR varies between ?1 and +2 dB and ZH is generally greater than 50 dBZ. The value of ZH peaks at around 60 dBZ or more when ZDR is in the range ?0.5 to 0 dB and 1.5 to 2 dB at 1.5 km and 2 km below the 0°C level, respectively. These and other features of ZH and ZDR are interpreted in terms of the size, shape and fall behavior of the hailstones using the dual wavelength ratio and the linear depolarization ratio radar measurements together with results from Battering computations. The negative ZDR, regions in this storm are inferred to be most likely composed of melting hailstones with sizes predominantly in the 12 to 40 mm range, which fall with their larger dimensions aligned (on the average) vertically. The positive ZDR values greater than 1 dB are concluded to be due to melting hailstones with sizes less than 12 mm, which fall with their larger dimensions aligned (on the average) horizontally.