A new application of the boundary element method to compute the single-scattering properties of complex ice crystals in the microwave

Abstract

The Boundary Element Method (BEM) is being applied to compute the single-scattering properties of randomly oriented complex rosette ice aggregates at the frequencies of 50, 183, 243 and 664 GHz, for the temperatures 190, 230, and 270 K. The rosette aggregates were generated using a Monte Carlo model, and from the statistical runs, 65 aggregates were selected that were within ±30% of an existing mass-dimension relation that is consistent with the Met Office's cirrus microphysics scheme in its weather and climate models. The generated 65 aggregates have maximum dimensions between 10 μm and approximately 1 cm. To compute efficiently their single-scattering properties using BEM, random orientation is approximated by rotating the incident wave about the scatterer rather than the other way around as is done in all other electromagnetic methods. This exploits the BEM linear matrix equation (i.e. Ax=b) by only needing to compute the matrix A once, leaving the less computationally demanding b to change. We show that our representation of random orientation can accurately compute the single-scattering properties of non-axisymmetric particles to within 1 or 2% of T-matrix solutions, and we compare the solutions found for our rosette aggregate models with other commonly used models in the microwave.