The enhancement of lidar backscattering by horizontally oriented ice crystal plates in cirrus clouds

The backscattering of radiation at 0.532 and 1.064 μm wavelengths by quasi-horizontally oriented hexagonal ice plates is investigated. The geometric optics ray tracing method is not applicable to the scattering problem associated with oriented ice crystals (in particular, in backscattering direction) because of the singularity of the ray-tracing technique. In the present study, we solve the scattered field of quasi-horizontally oriented ice plates using an approach based on electromagnetic wave theory. The effect of side faces of a plate on the internal field inside the particle is ignored. This is a reasonable approximation under the condition that the ratio of particle diameter to its length is large or the tilt of the particle symmetric axis from the zenith is small. Preliminary results show very strong resonant oscillations of backscattering cross section versus size parameter. The bulk backscattering intensity has been calculated by including size distribution and a random tilt of particle symmetric axis within a small angular region (2°).