Spectral properties of mesospheric ice clouds: Evidence for nonspherical particles

[1] We discuss spectrally resolved measurements of the light scattering by mesospheric ice particles from lidars and satellite-borne instruments in order to test whether Gaussian particle size distributions predicted by microphysical models are consistent with these observations. This study shows that none of the considered data sets is consistent with this assumption as long as spherical particles are assumed whose scattering properties may be described by Mie scattering theory. In addition, lognormal size distributions fail to explain data sets obtained from the SME and SNOE satellite, again assuming spherical particles described by the Mie theory. However, considering needle- or plate-like spheroid-shaped particles with Gaussian size distributions, we find that particles with axial ratios of ∼0.2 and/or 5.0 allow us to find a consistent set of ice particle distribution parameters. This parameter set can simultaneously explain all considered observations and is in good agreement with microphysical model results. On the basis of these findings we suggest that nonspherical particle scattering theory be considered for the precise analysis of optical soundings of mesospheric ice particles.

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