Measurement of Attenuation and Radar Reflectivity in Melting Layer with Gound-based Ka-band Radars

Ice aggregates melt and become liquid water drops while they are falling through the height of 0°C and at the same time the dielectric constant of particles and falling velocity rapidly increase and the shapes are dramatically change . As a result the melting layers are observed as “bright” for radars in wide frequency. The attenuation and the equivalent radar reflectivity in melting layer show the process of changing physical property of melting precipitation particles. And such information will support estimating Z-R relationship about wet snow. It is important because the snow is almost wet in the area along the Sea of Japan where is well known as the heaviest snowfall region in Japan.
This study is a simultaneous measurement of attenuation coefficient (k) and equivalent radar reflectivity (Z_e) independently through melting layer using two Ka-band radars which has been developed by JAXA. Near identical two radars were installed along the slope of the mountain, with facing to each other as the beams completely match without any obstacles. Then two way measured reflectivity and total path 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 ice-core model calculation.

The results are used to evaluate the scattering/attenuation assumptions in the dual-frequency precipitation radar (DPR) aboard the Global Precipitation Measurement (GPM) core satellite.