Modeling radar backscattering from melting snowflakes
at C-band using DDA and TMM
J. Tyynelä*,1, J. Leinonen2, D. Moisseev1 and T. Nousiainen1
- 1 Department of Physics, University of Helsinki, P.O. box 14, FI-00014 Helsinki, Finland.
- 2 Finnish Meteorological Institute, P.O. box 503, FI-00101 Helsinki, Finland.
We model radar backscattering in the C-band from fluffy snowflakes at early stages of melting using both the discrete-dipole approximation (DDA) and the T-matrix method (TMM). DDA approximates the particle as a cubic lattice of dipoles, while TMM is an exact method for nonspherical particles. To simulate falling snowflakes at early melting, the particles are modeled as oriented oblate spheroids and have melted only at the bottom part. We use two different dipole distributions for DDA; random single dipoles and dipole groups consisting of 4×4×4 dipoles. We find that even a very fluffy particle shows resonance features for most radar parameters. Using the Maxwell-Garnett effective medium approximation in TMM computations seems to match DDA well for all sizes studied. Small amount of inhomogeneously distributed water has a negligible effect on most radar parameters for both DDA and TMM. Only the specific differential phase KDP shows clear deviation between DDA and TMM. Using dipole groups instead of single dipoles to approximate a fluffy snowflake seems to effect KDP the most.
- * Corresponding author