Hail detection using S- and C-band radar reflectivity difference

In reflectivity fields observed with conventional radar networks, hailstorm identification is not easy. In the present paper, a hailstorm detection method using two single-wavelength radars located far from each other is discussed. The two radars, C and S bands, respectively, are about 200 km apart. Because large hailstones are non-Rayleigh scatterers, the distribution of the dual-wavelength reflectivity ratio is shown to display an identifying signal for hail-bearing storms. The relevance and sensitivity of the proposed hail detection algorithm is first analyzed from a simulation of 10.7- and 5.3-cm radar observations. Various convective storm conditions, differing by the horizontal shape and the nature of precipitation, are considered, notably rain and hail with hailstones of different diameters, dry or coated with liquid water. The attenuation for the radar-target propagation path and inside the target is also taken into account. The dual-wavelength reflectivity ratio for all the simulated radar observations shows that the proposed criterion enables an identification of the hail-bearing storms. The algorithm is then applied to real cases of storms observed with the French meteorological radar network. The comparison of the hail areas identified by the dual-wavelength algorithm with the hail impacts observed with ground-based hailpad networks confirms the ability of the algorithm to detect the hail-bearing cells in proper time and place. It is concluded that the dual-wavelength reflectivity ratio has a potential for hail detection, using an operational radar network organized in such a way that the convective field can be simultaneously observed with both an S-band and a C-band radar.