Potential uses of the differential propagation phase constant to estimate raindrop and hailstone size distributions

One of the Doppler radars operated by the National Severe Storms Laboratory can measure the difference between propagation phase constants K_Dp at horizontal and vertical polarization. This study examines the use of this parameter K _Dp in addition to the reflectivity factor Z_H and the differential reflectivity Z_DR, to obtain information about rain and hail. It is shown from theory and experiments that a third parameter of the drop size distribution, obtained from K_DP, can be used to support Z _DR measurement and/or to point out mixed-phase hydrometeors. Quantitative information on hail size distribution can be obtained for small hailstones when their major axes are nearly vertically aligned, giving rise to negative Z_DR and K_DP values