Calculations of Doppler Radar Velocity Spectrum Parameters for a Mixture of Rain and Hail

Abstract

The radar reflectivity factors, the reflectivity-weighted mean terminal velocities (VT), and the standard deviations (σv) of the resulting Doppler spectra, were computed for specified size distributions of rain, dry and wet ice spheres (taken to be hailstones), and rain with hail. Unambigous estimates of the mean velocity and standard deviation can be obtained from a radar measurement of reflectivity for rain alone and for dry ice spheres as a function of maximum sphere size. The results for wet ice spheres are strongly dependent on the thickness of the liquid water coating on the ice core. When rain and hail coexist, large values of reflectivity are associated with large ranges of VT and σv. If the shape of the hail size distribution is known, an independent measurement of the maximum hailstone diameter or a knowledge of the standard deviation of the observed Doppler velocity spectrum can reduce the uncertainty in estimates of VVT.