Radiowave Scattering Characteristics of Melting Layer Measured by a Dual Ka-band Radar System

Abstract

Specific attenuation and equivalent radar reflectivity in a melting layer were measured using a dual Ka-band radar system. The system consists of two identically designed Ka-radars. When the two radars are arranged to face each other and a precipitation system comes between the two radars, they observe the system from opposite directions. The radar echoes suffer from rain attenuation, which appears symmetrically in both radar echo profiles. By differentiating measured radar reflectivity with range, the specific attenuation (k) can be estimated. After obtaining the specific attenuation, the equivalent radar reflectivity (Z_e) is estimated. Melting layer observations were conducted on a slope of Mt. Zao, Japan. In the melting layer, the specific attenuation and the equivalent radar reflectivity vary considerably along the radio path. The relationship between k and Z_e showed interesting characteristics that appear in a loop-shape on a k-Z_e diagram. A simple theoretical study using the Rayleigh and Mie scattering theories for melting snow spheres showed that the basic loop-shape is because of the change in permittivity of precipitation particles during melting. The loop-shape is greatly expanded by the change of the particle size. The Mie effect, which is significant for large precipitation particles, slightly modifies the loop-shape by reducing backscattering cross sections. The results also explain the shelf-like profile instead of the peak-like for Z_e.