Modeling radar backscattering from melting snowflakes using spheroids with nonuniform distribution of water

- We model backscattering from spheroidal melting snowflakes at C, Ku, Ka, and W bands.
- We study the effect of anisotropic distribution of meltwater in the snow particles.
- We find systematic, but relatively small differences for the backscattering properties.
- We find that the aspect ratio and resonance peaks have a bigger effect than anisotropic distribution of water.
- Anisotropic distribution of water is not significant for radar observations at early stages of melting.

In a number of studies it is reported that at the early stages, melting of aggregate snowflakes is enhanced at lower parts. In this paper, the manifestation of the resulting nonuniform distribution of water is studied for radar backscattering cross sections at C, Ku, Ka and W bands. The melting particles are described as spheroids with a mixture of water and air at the bottom part of the particle and a mixture of ice and air at the upper part. The radar backscattering is modeled using the discrete-dipole approximation in a horizontally pointing geometry. The results are compared to the T-matrix method, Mie theory, and the Rayleigh approximation using the Maxwell Garnett mixing formula. We find that the differential reflectivity and the linear depolarization ratio show systematic differences between the discrete-dipole approximation and the T-matrix method, but that the differences are relatively small. The horizontal cross sections show only small differences between the methods with the aspect ratio and the presence of resonance peaks having a larger effect on it than the nonuniform distribution of water. Overall, the effect of anisotropic distribution of water, reported for early stages of melting, is not significant for radar observations at the studied frequencies.