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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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 |
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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 |
op_rights |
undefined |
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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1766194968498536448 |