Backscattering by hexagonal ice crystals of cirrus clouds

Abstract

Light backscattering by randomly oriented hexagonal ice crystals of cirrus clouds is considered within the framework of the physical-optics approximation. The fine angular structure of all elements of the Mueller matrix in the vicinity of the exact backward direction is first calculated and discussed. In particular, an approximate equation for the differential scattering cross section is obtained. Its simple spectral dependence is discussed. Also, a hollow of the linear depolarization ratio around the exact backward direction inherent to the long hexagonal columns is revealed.

Backscattering Properties of Nonspherical Ice Particles Calculated by Geometrical-Optics-Integral-Equation Method

“…This changes in L and δ can be explained as follows. The backscattered light by hexagonal plates and columns are composed of specular and corner-reflection terms [7]. The corner-reflection term originates from refraction/reflection events at orthogonal faces of the hexagonal crystals.…”

Backscatter ratios for arbitrary oriented hexagonal ice crystals of cirrus clouds

“…As was discussed earlier [11,12], the backscatter is determined by two components. The first one is the specular term that consists of the plane-parallel beams leaving a crystal surface at the reflection direction n determined by the equation n z − 2z · NN (for the plates).…”

“…Such a singularity was an obstacle to calculating these backscatter quantities using the common ray-tracing simulation. Recently, this singularity was eliminated within the physical-optics approximation [11,12]. In this Letter, we calculate the ratios of Eq.…”

The technique for solving the problem of light backscattering by ice crystals of cirrus clouds by the physical optics method for a lidar with zenith scanning

“…Then, for the above-mentioned law of the distribution over orientations, the beams are sorted by the contribution to the intensity and only those contributing 99.9% (in some cases, 99.5%) are selected. At the same stage, mutual trajectories described in detail in [32,33] are determined and grouped.…”

“…The obtained matrix (28) is averaged over angles of particle rotation α according to the expression (33) Note that in the case of a vertical lidar (θ = 0) we have σ = β and φ = α and expression (33) takes the classical form of averaging over the angle of rotation (34) …”