A scattering phase function for ice cloud: Tests of applicability using aircraft and satellite multi-angle multi-wavelength radiance measurements of cirrus

Abstract

A parametrization of the Henyey-Greenstein scattering phase function is presented for application to aircraft and satellite remote sensing of cirrus-cloud bulk and microphysical properties at non-absorbing and absorbing wavelengths. The phase function is based initially around a non-absorbing laboratory-measured phase function between scattering angles of 30° and 180°, although at scattering angles greater than 95° the phase function is made constant with scattering angle. This 'analytic' phase function has an asymmetry parameter value of 0.80 at non-absorbing wavelengths. This analytic phase function is tested using aircraft-based transmission radiance measurements at the wavelengths of 0.55 μm, 0.87 μm, 1.6 μm and 3.7 μm between scattering angles of 10° and 120°, and satellite retrievals of cirrus-cloud spherical albedo at the wavelength of 0.67 μm between scattering angles of 60° and 180°. The analytic phase function reproduces both aircraft and satellite measurements well, and is shown to be a distinct improvement over single-crystal model phase functions representing both small and large crystals in terms of angular scattering pattern and retrieved optical thickness.