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Evaluation of the Rayleigh–Gans approximation for microwave scattering by rimed snowflakes
Author(s) -
Lein Jussi,
Kneifel Stefan,
Hogan Robin J.
Publication year - 2018
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.3093
Subject(s) - snowflake , rayleigh scattering , scattering , microwave , discrete dipole approximation , computational physics , materials science , dipole , physics , optics , meteorology , quantum mechanics , snow
We have evaluated the applicability of the Rayleigh–Gans approximation (RGA) and self‐similar Rayleigh–Gans approximation (SSRGA) for microwave scattering by rimed snowflakes. This study extends previous findings that showed that, for unrimed snowflakes, the RGA is in good agreement with the discrete dipole approximation (DDA), which we used as a reference method. When riming is introduced, the RGA‐derived scattering properties of individual snowflakes deviate significantly – up to 20–25 dB for the backscattering cross‐section in the W band – from the corresponding DDA results. In contrast, the average scattering properties given by RGA are in good agreement with DDA for all but the most heavily rimed snowflakes: the mean bias in the backscattering cross‐section rarely exceeds 1 dB for light and moderate riming. We also found that an adjustment that accounts for the non‐spherical shapes of ice crystals can help eliminate the small constant bias found in RGA in earlier studies. The SSRGA approximates the RGA results with good accuracy at all degrees of riming, indicating that it, too, can be used with up to moderately rimed snowflakes.