Light scattering by ice crystals of cirrus clouds: From exact numerical methods to physical-optics approximation

- The physical-optics approximation and two exact numerical methods are compared.
- The number of orientations required for appropriate spatial averaging was estimated.
- The accuracy of the physical-optics is estimated as 95% for averaged Mueller matrix.

The problem of light scattering by ice crystals of cirrus clouds is considered in the case of a hexagonal ice plate with different distributions over crystal orientations. The physical-optics approximation based on (E, M)-diffraction theory is compared with two exact numerical methods: the finite difference time domain (FDTD) and the discontinuous Galerkin time domain (DGTD) in order to estimate its accuracy and limits of applicability. It is shown that the accuracy of the physical-optics approximation is estimated as 95% for the averaged backscattering Mueller matrix for particles with size parameter more than 120. Furthermore, the simple expression that allows one to estimate the minimal number of particle orientations required for appropriate spatial averaging has been derived.