Attenuation and Radar Reflectivity in Melting Layer measured with Ground-based Ka-band Radars

Ice aggregates melt to liquid water drops while they are falling through the 0°C layer (melting layer). In the melting layer, dielectric constant of particles and falling velocity rapidly increase and the size and shapes dramatically change. The specific attenuation (k) and the equivalent radar reflectivity (Z_e) in the melting layer reflect the process in melting of precipitation particles. Understanding the processis essential for estimating Z-R relationship of wet snow. Estimation of rain rate of wet snow is particularly important for Japan, since the heaviest snow region along the Sea of Japan suffers from wet snow. Identically designed two Ka-band radars were installed along the slope of a mountain infacing to each other From the two echo profiles radar, reflectivity and attenuation are obtained. Since calculation of k includes double differences along the radio path, the result is sensitive to the experimental parameters. Parameter tunings in data analysis including small change of radar elevation angles, etc are applied. After the parameter tuning, the k and Z_e are reasonably obtained for clear melting layers, where Z_e　has a shape of a shelf or convex, and k had a peak at the shoulder of the shelf. The results are qualitatively consistent with ground-based particle measurements and simple melting sphere model calculation. The results are used to evaluate the scattering/attenuation assumptions in the rain estimation algorithms of the dual-frequency precipitation radar (DPR) aboard the Global Precipitation Measurement (GPM) core satellite.