Technical Note: Optical properties of desert aerosol with non-spherical mineral particles: data incorporated to OPAC

Mineral particles, in general, are not spheres and so the assumption of spherical particles, instead of more realistic shapes, has significant effects on modeled optical properties and therefore on remote-sensing procedures for desert aerosol and the derived radiative forcing. Thus, in a new version...

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Bibliographic Details
Published in:Atmospheric chemistry and physics 2015-05, Vol.15 (10), p.5947-5956
Main Authors: Koepke, P, Gasteiger, J, Hess, M
Format: Article
Language:English
Subjects:
Aerosol optical properties
Aerosols
Analysis
Aspect ratio
Backscatter
Backscattering
Datasets
Deserts
Deviation
Dust
Humidity
Mathematical models
Mineral particles
Minerals
Optical properties
Particle size
Radiative forcing
Refractivity
Remote sensing
Scattering angle
Scattering functions
Software packages
Spectra
Spheroids
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Description
Summary:Mineral particles, in general, are not spheres and so the assumption of spherical particles, instead of more realistic shapes, has significant effects on modeled optical properties and therefore on remote-sensing procedures for desert aerosol and the derived radiative forcing. Thus, in a new version of the database OPAC (Optical Properties of Aerosols and Clouds; Hess et al., 1998), the optical properties of the mineral particles are modeled describing the particles as spheroids with size dependent aspect ratio distributions, but with the size distributions and the spectral refractive indices not changed against the previous version of OPAC. The spheroid assumption is known to substantially improve the scattering functions but pays regard to the limited knowledge on particle shapes in an actual case. The relative deviations of the optical properties of non-spherical mineral particles from those of spherical particles are for the phase function in the solar spectral range up to +60% at scattering angles of about 130° and up to -60% in the backscatter region, but less than 2% for the asymmetry parameter. The deviations are generally small in the thermal infrared and for optical properties that are independent of the scattering angle. The improved version of OPAC (4.0) is freely available at www.rascin.net.
ISSN:1680-7324
1680-7316
1680-7324
DOI:10.5194/acp-15-5947-2015