Kim 2006

Reference
Kim, M. J. (2006). Single scattering parameters of randomly oriented snow particles at microwave frequencies. Journal of Geophysical Research: Atmospheres, 111(D14).
Link to the database
Authors
Min-jeong Kim
Kim 2006
Model crystal habits considered in this study.

Specifications

Types of particles

pristine crystals

Frequencies

95 to 340 GHz

Scattering properties

Total extinction cross section, Asymmetry parameter, Total absorption cross section, Total scattering cross section

Sizes

Temperatures

Random orientations?

yes

Shapefiles included?

no

Scattering method(s)

DDA, T-matrix

Scattering method details

Summary

Description of the work

To develop a generally applicable fast and accurate parameterization method for computations of single scattering parameters at microwave frequencies requires a thorough knowledge of how the ice particle shape affects the scattering parameters. This study computes single scattering parameters (scattering cross sections (Csca), absorption cross sections (Cabs), and asymmetry factors) of various nonspherical snow particles using the discrete dipole approximation (DDA) method and the T-matrix method to examine the sensitivity of scattering parameters to snow particles at frequencies between 95 GHz and 340 GHz. Results show that Csca/πreff2, Cabs/πreff2, and asymmetry factors of complex particles at a fixed size parameter x = 2πreff/λ do not depend on the specific particle shapes when x is less than about 2.5. Here λ is the wavelength and reff is the radius of equal-volume ice spheres. The Mie theory may be used to compute the single scattering parameters of randomly oriented snow particles if radius of equal-volume ice spheres reff is known over this range. On the other hand, when x > 2.5, scattering parameters of nonspherical particles are sensitive to the particle shapes because they are in an anomalous diffraction regime. In this regime, particles have a smaller projected area for a given volume so that the “unfavorable” interference effect grows, resulting in smaller minimum values of scattering cross sections and asymmetry factors. Single scattering parameters averaged over a Gamma size distribution show that scattering coefficients are sensitive to shapes and that differences are larger than 10% when πDm/λ; the size parameter of the median mass diameter (Dm) is greater than 1. Single scattering albedo values do not show significant differences over most size parameter ranges considered in this study. Asymmetry factors are sensitive to particle shapes when πDm/λ is greater than 2.
Kim 2006
Comparisons of scattering cross sections (Csca), absorption cross sections (Cabs), and asymmetry factors for different snow particle models. The x axis shows the size parameter defined as x = 2πreff/λ, where reff is the radius of equal-V spheres and λ is the wavelength. Particles are all assumed to be randomly oriented. Solid lines show the Mie calculation results for spheres, and different symbols show the DDA calculated scattering parameters of different particle shapes (open circles, C1; crosses, C2; triangles, C3; squares, C4).
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