The impact of ice particle roughness on the scattering phase matrix

The goal of this study is to explore the influence of ice particle habit (or shape) and surface roughness on the scattering phase matrix As an example, reported here are the results for two wavelengths: 067 and 1.61 mu m For this effort, a database of single-scattering properties has been computed for a set of habits including hexagonal plates, hollow and solid columns, hollow and solid 3D bullet rosettes, droxtals, aggregates of solid columns, and aggregates of plates. The database provides properties for each of the habits at 101 wavelengths between 045 and 224 pm for smooth, moderately roughened, and severely roughened particles. At each wavelength, the scattering properties are provided at 233 discrete particle diameters ranging from 2 to 10,000 pm. A single particle size distribution from a very cold ice cloud sampled during the CRYSTAL-FACE field campaign (T-ctd=-76 degrees C) is used to illustrate the influence of habit and roughness on the phase matrix In all, four different habit mixtures are evaluated The nonzero elements of the phase matrix are shown to be quite sensitive to the assumed habit, particularly in the case of -P-12/P-11 that is associated with the degree of linear polarization of scattered radiation Surface roughness is shown to smooth out maxima in the scattering phase function and in the other elements of the, phase matrix, consistent with other studies. To compare with the theoretical simulations of the phase matrix for smooth and roughened particles, a full year of cloud-aerosol lidar with orthogonal polarization (CALIOP) data from 2008 is analyzed to provide global statistics on the values of P-11 and P-22/P-11 in the backscattering direction In a comparison of two of the habit mixtures (one used for MODIS Collection 5 and another that incorporates new habits including hollow bullet rosettes and aggregates of plates) with the CALIOP data, the values for P-11 are higher regardless of the degree of particle surface roughness, and the values for P-22/P-11 are lower than those for CALIOP. Further investigation is warranted to better understand this discrepancy. (C) 2010 Elsevier Ltd. All rights reserved.