Light scattering by fractal roughness elements on ice crystal surfaces

Atmospheric ice crystals scatter sunlight, affecting Earth’s climate through the radiation properties of cirrus clouds. Naturally occurring surface roughness and its effect on scattering remain largely unknown. Scattering by with rough surfaces is studied placing a finite, thin surface-roughness element an infinitely large, planar vacuum-ice boundary. The elements are generated using statistical model based fractional Brownian motion. horizontal scale described Hurst exponent H vertical root-mean-square parameter Rq. computations performed mode Discrete Dipole Approximation software ADDA (version 1.34b). Several incident directions for wavelength 0.5 µm from both above below studied. A refractive index m=1.313+i5.889×10−10 used throughout computations. Results averaged over ten realizations specific H, Rq-pair. compared to that corresponding smooth elements. rougher is, more scattered intensity transmitted surface. have distinctively smoother angular distributions degree linear polarization than their counterparts. Also, it found while itself affects polarization, exact morphology does not seem significant effect. Rq has larger light results H. Enhanced detected in nearly parallel boundary within medium. phenomenon explained strong internal reflection mechanism. roughness, along methodology here, could be incorporated into geometric optics ray-tracing large other particles.