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Rayleigh scattering by hexagonal ice crystals and the interpretation of dual-polarisation radar measurements

Westbrook, C. D. ORCID: (2014) Rayleigh scattering by hexagonal ice crystals and the interpretation of dual-polarisation radar measurements. Quarterly Journal of the Royal Meteorological Society, 140 (683). pp. 2090-2096. ISSN 1477-870X

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To link to this item DOI: 10.1002/qj.2262


Dual-polarisation radar measurements provide valuable information about the shapes and orientations of atmospheric ice particles. For quantitative interpretation of these data in the Rayleigh regime, common practice is to approximate the true ice crystal shape with that of a spheroid. Calculations using the discrete dipole approximation for a wide range of crystal aspect ratios demonstrate that approximating hexagonal plates as spheroids leads to significant errors in the predicted differential reflectivity, by as much as 1.5 dB. An empirical modification of the shape factors in Gans's spheroid theory was made using the numerical data. The resulting simple expressions, like Gans's theory, can be applied to crystals in any desired orientation, illuminated by an arbitrarily polarised wave, but are much more accurate for hexagonal particles. Calculations of the scattering from more complex branched and dendritic crystals indicate that these may be accurately modelled using the new expression, but with a reduced permittivity dependent on the volume of ice relative to an enclosing hexagonal prism.

Item Type:Article
Divisions:Science > School of Mathematical, Physical and Computational Sciences > Department of Meteorology
ID Code:40877
Uncontrolled Keywords:microwave scattering;ice crystal;dual polarisation
Publisher:Royal Meteorological Society

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