Quantification of ice cloud particle roughness from multi-angle satellite observations

Abstract:

The phase function calculated by an improved geometric optics method (IGOM) is applied to MISR
(Multi-angle Imaging SpectroRadiometer) observation with a focus on the effect of particle roughness.
Previous studies suggest that the simulated cloud directional reflectivity values
match with observations when a certain degree of roughness is introduced in the computation of the
single-scattering properties. However, the optimal value of the degree of particle surface
roughness and its geographical variability are not well understood. This study introduces a new
parameter, the effective roughness, to estimate the degree of roughness to describe observed
cloud directional reflectivity and to evaluate its latitudinal variation. Sensitivity studies
show that the effective roughness well quantifies the impact of roughness on the bulk scattering properties,
particularly, the effect on the asymmetry factor and phase function. Utilizing the multi-angle imaging by MISR,
we demonstrate that the effective roughness can be determined with satellite observations.