Comparisons of electromagnetic scattering properties of real hailstones and spheroids

The S-band scattering properties of these hailstones were calculated with the discrete dipole approximation (DDA). For comparison, scattering properties of spheroidal approximations of each hailstone (with identical maximum and minimum dimensions and mass) were calculated with the T matrix. The polarimetric radar variables have errors when using spheroids, even for small hail.

Spheroids generally have smaller variations in the polarimetric variables than the real hailstones. This increased variability is one reason why the correlation coefficient tends to be lower in observations than in forward-simulated cases using spheroids. Backscatter differential phase delta also is found to have large variance, particularly for large hailstones.

Irregular hailstones with a thin liquid layer produce enhanced and more variable values for reflectivity factor at horizontal polarization Z(HH), differential reflectivity Z(DR), specific differential phase K-DP, linear depolarization ratio (LDR), and delta compared with dry hailstones; is also significantly reduced.