dorsal/arxiv
View SchemaRadar scattering by aggregate snowflakes
| Authors | C. D. Westbrook, R. C. Ball, P. R. Field |
|---|---|
| Categories | |
| ArXiv ID | physics/0505083 |
| URL | https://arxiv.org/abs/physics/0505083 |
| DOI | 10.1256/qj.05.82 |
Abstract
The radar scattering properties of realistic aggregate snowflakes have been calculated using the Rayleigh-Gans theory. We find that the effect of the snowflake geometry on the scattering may be described in terms of a single universal function, which depends only on the overall shape of the aggregate and not the geometry or size of the pristine ice crystals which compose the flake. This function is well approximated by a simple analytic expression at small sizes; for larger snowflakes we fit a curve to our numerical data. We then demonstrate how this allows a characteristic snowflake radius to be derived from dual-wavelength radar measurements without knowledge of the pristine crystal size or habit, while at the same time showing that this detail is crucial to using such data to estimate ice water content. We also show that the `effective radius', characterising the ratio of particle volume to projected area, cannot be inferred from dual-wavelength radar data for aggregates. Finally, we consider the errors involved in approximating snowflakes by `air-ice spheres', and show that for small enough aggregates the predicted dual wavelength ratio typically agrees to within a few percent, provided some care is taken in choosing the radius of the sphere and the dielectric constant of the air-ice mixture; at larger sizes the radar becomes more sensitive to particle shape, and the errors associated with the sphere model are found to increase accordingly.
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"abstract": "The radar scattering properties of realistic aggregate snowflakes have been\ncalculated using the Rayleigh-Gans theory. We find that the effect of the\nsnowflake geometry on the scattering may be described in terms of a single\nuniversal function, which depends only on the overall shape of the aggregate\nand not the geometry or size of the pristine ice crystals which compose the\nflake. This function is well approximated by a simple analytic expression at\nsmall sizes; for larger snowflakes we fit a curve to our numerical data. We\nthen demonstrate how this allows a characteristic snowflake radius to be\nderived from dual-wavelength radar measurements without knowledge of the\npristine crystal size or habit, while at the same time showing that this detail\nis crucial to using such data to estimate ice water content. We also show that\nthe `effective radius\u0027, characterising the ratio of particle volume to\nprojected area, cannot be inferred from dual-wavelength radar data for\naggregates. Finally, we consider the errors involved in approximating\nsnowflakes by `air-ice spheres\u0027, and show that for small enough aggregates the\npredicted dual wavelength ratio typically agrees to within a few percent,\nprovided some care is taken in choosing the radius of the sphere and the\ndielectric constant of the air-ice mixture; at larger sizes the radar becomes\nmore sensitive to particle shape, and the errors associated with the sphere\nmodel are found to increase accordingly.",
"arxiv_id": "physics/0505083",
"authors": [
"C. D. Westbrook",
"R. C. Ball",
"P. R. Field"
],
"categories": [
"physics.ao-ph",
"physics.geo-ph"
],
"doi": "10.1256/qj.05.82",
"title": "Radar scattering by aggregate snowflakes",
"url": "https://arxiv.org/abs/physics/0505083"
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