Parameterization of single-scattering properties of snow
Snow consists of non-spherical grains of various shapes and sizes. Still, in many radiative transfer applications, single-scattering properties of snow have been based on the assumption of spherical grains. More recently, second-generation Koch fractals have been employed. Wh...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2015-06-01
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| Series: | The Cryosphere |
| Online Access: | http://www.the-cryosphere.net/9/1277/2015/tc-9-1277-2015.pdf |
| _version_ | 1811239611278557184 |
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| author | P. Räisänen A. Kokhanovsky G. Guyot O. Jourdan T. Nousiainen |
| author_facet | P. Räisänen A. Kokhanovsky G. Guyot O. Jourdan T. Nousiainen |
| author_sort | P. Räisänen |
| collection | DOAJ |
| description | Snow consists of non-spherical grains of various shapes and
sizes. Still, in many radiative transfer applications,
single-scattering properties of snow have been based on the assumption
of spherical grains. More recently, second-generation Koch fractals
have been employed. While they produce a relatively flat 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 <i>r</i><sub>vp</sub>. Parameterization equations are
developed for λ = 0.199–2.7 μm and
<i>r</i><sub>vp</sub> = 10–2000 μm, which express the
single-scattering co-albedo β, the asymmetry parameter <i>g</i> and
the phase function <i>P</i><sub>11</sub> as functions of the size parameter and the
real and imaginary parts of the refractive index. The
parameterizations are analytic and simple to use in radiative transfer
models. Compared to the reference values computed for the OHC, the
accuracy of the parameterization is very high for β and
<i>g</i>. 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 to spheres and distorted Koch fractals. |
| first_indexed | 2024-04-12T13:04:09Z |
| format | Article |
| id | doaj.art-d97862af908241f89001bb4193e02d22 |
| institution | Directory Open Access Journal |
| issn | 1994-0416 1994-0424 |
| language | English |
| last_indexed | 2024-04-12T13:04:09Z |
| publishDate | 2015-06-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | The Cryosphere |
| spelling | doaj.art-d97862af908241f89001bb4193e02d222022-12-22T03:32:06ZengCopernicus PublicationsThe Cryosphere1994-04161994-04242015-06-01931277130110.5194/tc-9-1277-2015Parameterization of single-scattering properties of snowP. Räisänen0A. Kokhanovsky1G. Guyot2O. Jourdan3T. Nousiainen4Finnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, FinlandEUMETSAT, Eumetsat Allee 1, 64295 Darmstadt, GermanyLaboratoire de Météorologie Physique (LaMP) Université Blaise Pascal/CNRS/OPGC, 24 avenue des Landais, 63177 Aubiére CEDEX, FranceLaboratoire de Météorologie Physique (LaMP) Université Blaise Pascal/CNRS/OPGC, 24 avenue des Landais, 63177 Aubiére CEDEX, FranceFinnish Meteorological Institute, P.O. Box 503, 00101 Helsinki, FinlandSnow consists of non-spherical grains of various shapes and sizes. Still, in many radiative transfer applications, single-scattering properties of snow have been based on the assumption of spherical grains. More recently, second-generation Koch fractals have been employed. While they produce a relatively flat 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 <i>r</i><sub>vp</sub>. Parameterization equations are developed for λ = 0.199–2.7 μm and <i>r</i><sub>vp</sub> = 10–2000 μm, which express the single-scattering co-albedo β, the asymmetry parameter <i>g</i> and the phase function <i>P</i><sub>11</sub> as functions of the size parameter and the real and imaginary parts of the refractive index. The parameterizations are analytic and simple to use in radiative transfer models. Compared to the reference values computed for the OHC, the accuracy of the parameterization is very high for β and <i>g</i>. 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 to spheres and distorted Koch fractals.http://www.the-cryosphere.net/9/1277/2015/tc-9-1277-2015.pdf |
| spellingShingle | P. Räisänen A. Kokhanovsky G. Guyot O. Jourdan T. Nousiainen Parameterization of single-scattering properties of snow The Cryosphere |
| title | Parameterization of single-scattering properties of snow |
| title_full | Parameterization of single-scattering properties of snow |
| title_fullStr | Parameterization of single-scattering properties of snow |
| title_full_unstemmed | Parameterization of single-scattering properties of snow |
| title_short | Parameterization of single-scattering properties of snow |
| title_sort | parameterization of single scattering properties of snow |
| url | http://www.the-cryosphere.net/9/1277/2015/tc-9-1277-2015.pdf |
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