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| Titel |
Parameterization of single-scattering properties of snow |
| VerfasserIn |
Petri Räisänen, Alexander Kokhanovsky, Gwennole Guyot, Olivier Jourdan, Timo Nousiainen |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250104475
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| Publikation (Nr.) |
 EGU/EGU2015-3895.pdf |
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| Zusammenfassung |
| Snow consists of non-spherical ice grains of various shapes and sizes, which are surrounded
by air and sometimes covered by films of liquid water. Still, in many studies, homogeneous
spherical snow grains have been assumed in radiative transfer calculations, due to the
convenience of using Mie theory. More recently, second-generation Koch fractals have been
employed. While they produce a relatively flat scattering phase function typical of
deformed non-spherical particles, this is still a rather ad-hoc choice. Here, angular
scattering measurements for blowing snow conducted during the CLimate IMpacts of
Short-Lived pollutants In the Polar region (CLIMSLIP) campaign at Ny Ålesund,
Svalbard, are used to construct a reference phase function for snow. Based on this phase
function, an optimized habit combination (OHC) consisting of severely rough (SR)
droxtals, aggregates of SR plates and strongly distorted Koch fractals is selected. The
single-scattering properties of snow are then computed for the OHC as a function
of wavelength λ and snow grain volume-to-projected area equivalent radius rvp.
Parameterization equations are developed for λ=0.199–2.7 μm and rvp = 10–2000 μm,
which express the single-scattering co-albedo β, the asymmetry parameter g and
the phase function as functions of the size parameter and the real and imaginary
parts of the refractive index. Compared to the reference values computed for the
OHC, the accuracy of the parameterization is very high for β and g. This is also
true for the phase function parameterization, except for strongly absorbing cases
(β > 0.3). Finally, we consider snow albedo and reflected radiances for the suggested
snow optics parameterization, making comparisons with spheres and distorted Koch
fractals.
Further evaluation and validation of the proposed approach against (e.g.) bidirectional
reflectance and polarization measurements for snow is planned. At any rate, it seems
safe to assume that the OHC selected here provides a substantially better basis for
representing the single-scattering properties of snow than spheres do. Moreover, the
parameterizations developed here are analytic and simple to use, and they can also be
applied to the treatment of dirty snow following (e.g.) the approach of Kokhanovsky
(The Cryosphere, 7, 1325–1331, doi:10.5194/tc-7-1325-2013, 2013). This should
make them an attractive option for use in radiative transfer applications involving
snow. |
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