Influence of grain shape on light penetration in snow

The energy budget and the photochemistry of a snowpack depend greatly on the penetration of solar radiation in snow. Below the snow surface, spectral irradiance decreases exponentially with depth with a decay constant called the asymptotic flux extinction coefficient. As with the albedo of the snowp...

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Published in:The Cryosphere
Main Authors: Q. Libois, G. Picard, J. L. France, L. Arnaud, M. Dumont, C. M. Carmagnola, M. D. King
Format: Article in Journal/Newspaper
Language:English
Published: Copernicus Publications 2013
Subjects:
geo
Online Access:https://doi.org/10.5194/tc-7-1803-2013
http://www.the-cryosphere.net/7/1803/2013/tc-7-1803-2013.pdf
https://doaj.org/article/da4c73df2dde4541a87a0d7995553213
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spelling fttriple:oai:gotriple.eu:oai:doaj.org/article:da4c73df2dde4541a87a0d7995553213 2023-05-15T13:43:55+02:00 Influence of grain shape on light penetration in snow Q. Libois G. Picard J. L. France L. Arnaud M. Dumont C. M. Carmagnola M. D. King 2013-11-01 https://doi.org/10.5194/tc-7-1803-2013 http://www.the-cryosphere.net/7/1803/2013/tc-7-1803-2013.pdf https://doaj.org/article/da4c73df2dde4541a87a0d7995553213 en eng Copernicus Publications 1994-0416 1994-0424 doi:10.5194/tc-7-1803-2013 http://www.the-cryosphere.net/7/1803/2013/tc-7-1803-2013.pdf https://doaj.org/article/da4c73df2dde4541a87a0d7995553213 undefined The Cryosphere, Vol 7, Iss 6, Pp 1803-1818 (2013) geo envir Journal Article https://vocabularies.coar-repositories.org/resource_types/c_6501/ 2013 fttriple https://doi.org/10.5194/tc-7-1803-2013 2023-01-22T18:03:55Z The energy budget and the photochemistry of a snowpack depend greatly on the penetration of solar radiation in snow. Below the snow surface, spectral irradiance decreases exponentially with depth with a decay constant called the asymptotic flux extinction coefficient. As with the albedo of the snowpack, the asymptotic flux extinction coefficient depends on snow grain shape. While representing snow by a collection of spherical particles has been successful in the numerical computation of albedo, such a description poorly explains the decrease of irradiance in snow with depth. Here we explore the limits of the spherical representation. Under the assumption of geometric optics and weak absorption by snow, the grain shape can be simply described by two parameters: the absorption enhancement parameter B and the geometric asymmetry factor gG. Theoretical calculations show that the albedo depends on the ratio B/(1-gG) and the asymptotic flux extinction coefficient depends on the product B(1-gG). To understand the influence of grain shape, the values of B and gG are calculated for a variety of simple geometric shapes using ray tracing simulations. The results show that B and (1-gG) generally covary so that the asymptotic flux extinction coefficient exhibits larger sensitivity to the grain shape than albedo. In particular it is found that spherical grains propagate light deeper than any other investigated shape. In a second step, we developed a method to estimate B from optical measurements in snow. A multi-layer, two-stream, radiative transfer model, with explicit grain shape dependence, is used to retrieve values of the B parameter of snow by comparing the model to joint measurements of reflectance and irradiance profiles. Such measurements were performed in Antarctica and in the Alps yielding estimates of B between 0.8 and 2.0. In addition, values of B were estimated from various measurements found in the literature, leading to a wider range of values (1.0–9.9) which may be partially explained by the limited accuracy ... Article in Journal/Newspaper Antarc* Antarctica The Cryosphere Unknown The Cryosphere 7 6 1803 1818
institution Open Polar
collection Unknown
op_collection_id fttriple
language English
topic geo
envir
spellingShingle geo
envir
Q. Libois
G. Picard
J. L. France
L. Arnaud
M. Dumont
C. M. Carmagnola
M. D. King
Influence of grain shape on light penetration in snow
topic_facet geo
envir
description The energy budget and the photochemistry of a snowpack depend greatly on the penetration of solar radiation in snow. Below the snow surface, spectral irradiance decreases exponentially with depth with a decay constant called the asymptotic flux extinction coefficient. As with the albedo of the snowpack, the asymptotic flux extinction coefficient depends on snow grain shape. While representing snow by a collection of spherical particles has been successful in the numerical computation of albedo, such a description poorly explains the decrease of irradiance in snow with depth. Here we explore the limits of the spherical representation. Under the assumption of geometric optics and weak absorption by snow, the grain shape can be simply described by two parameters: the absorption enhancement parameter B and the geometric asymmetry factor gG. Theoretical calculations show that the albedo depends on the ratio B/(1-gG) and the asymptotic flux extinction coefficient depends on the product B(1-gG). To understand the influence of grain shape, the values of B and gG are calculated for a variety of simple geometric shapes using ray tracing simulations. The results show that B and (1-gG) generally covary so that the asymptotic flux extinction coefficient exhibits larger sensitivity to the grain shape than albedo. In particular it is found that spherical grains propagate light deeper than any other investigated shape. In a second step, we developed a method to estimate B from optical measurements in snow. A multi-layer, two-stream, radiative transfer model, with explicit grain shape dependence, is used to retrieve values of the B parameter of snow by comparing the model to joint measurements of reflectance and irradiance profiles. Such measurements were performed in Antarctica and in the Alps yielding estimates of B between 0.8 and 2.0. In addition, values of B were estimated from various measurements found in the literature, leading to a wider range of values (1.0–9.9) which may be partially explained by the limited accuracy ...
format Article in Journal/Newspaper
author Q. Libois
G. Picard
J. L. France
L. Arnaud
M. Dumont
C. M. Carmagnola
M. D. King
author_facet Q. Libois
G. Picard
J. L. France
L. Arnaud
M. Dumont
C. M. Carmagnola
M. D. King
author_sort Q. Libois
title Influence of grain shape on light penetration in snow
title_short Influence of grain shape on light penetration in snow
title_full Influence of grain shape on light penetration in snow
title_fullStr Influence of grain shape on light penetration in snow
title_full_unstemmed Influence of grain shape on light penetration in snow
title_sort influence of grain shape on light penetration in snow
publisher Copernicus Publications
publishDate 2013
url https://doi.org/10.5194/tc-7-1803-2013
http://www.the-cryosphere.net/7/1803/2013/tc-7-1803-2013.pdf
https://doaj.org/article/da4c73df2dde4541a87a0d7995553213
genre Antarc*
Antarctica
The Cryosphere
genre_facet Antarc*
Antarctica
The Cryosphere
op_source The Cryosphere, Vol 7, Iss 6, Pp 1803-1818 (2013)
op_relation 1994-0416
1994-0424
doi:10.5194/tc-7-1803-2013
http://www.the-cryosphere.net/7/1803/2013/tc-7-1803-2013.pdf
https://doaj.org/article/da4c73df2dde4541a87a0d7995553213
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op_doi https://doi.org/10.5194/tc-7-1803-2013
container_title The Cryosphere
container_volume 7
container_issue 6
container_start_page 1803
op_container_end_page 1818
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