On the interpretation of an unusual in-situ measured ice crystal scattering phase function
1Met Office, FitzRoy Road, Exeter, EX1 3PB, UK
2Laboratoire de Météorologie Physique,UMR6016 CNRS/Université Blaise Pascal, Clermont-Ferrand, France
3Laboratoire de Météorologie Physique, Institut Universitaire de Technologie d'Allier, Montluçon, France
Abstract. In-situ Polar Nephelometer (PN) measurements of unusual ice crystal scattering phase functions were recently reported by Gayet et al. (2012). The ice crystal habits that produced the phase functions were small chain-like aggregates, which had on their surfaces, smaller quasi-spherical ice crystals. The measured-averaged phase functions were featureless, at scattering angles less than about 100°, but an ice bow-like feature was noted between the scattering angles of about 120° to 160°. The estimated asymmetry parameter was 0.78 ± 0.04.
In this paper, the phase function is interpreted in terms of a weighted habit mixture model. The best-fit model comprises of highly distorted ten element hexagonal ice aggregates, and the smaller quasi-spherical ice crystals are represented by Chebyshev ice particles. The weighted mean asymmetry parameter was found to be 0.81. It is argued that the Chebyshev-like ice particles are responsible for the ice bow-like feature and mostly dominate the scattered intensity measured by the PN. The results of this paper have important implications for climate modelling (energy balance of anvils) and the remote sensing of cirrus properties.