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...
Published in: | The Cryosphere |
---|---|
Main Authors: | , , , , , , |
Format: | Article in Journal/Newspaper |
Language: | English |
Published: |
Copernicus Publications
2013
|
Subjects: | |
Online Access: | https://doi.org/10.5194/tc-7-1803-2013 https://doaj.org/article/da4c73df2dde4541a87a0d7995553213 |
id |
ftdoajarticles:oai:doaj.org/article:da4c73df2dde4541a87a0d7995553213 |
---|---|
record_format |
openpolar |
spelling |
ftdoajarticles:oai:doaj.org/article:da4c73df2dde4541a87a0d7995553213 2023-05-15T13:38:57+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 2013-11-01T00:00:00Z https://doi.org/10.5194/tc-7-1803-2013 https://doaj.org/article/da4c73df2dde4541a87a0d7995553213 EN eng Copernicus Publications http://www.the-cryosphere.net/7/1803/2013/tc-7-1803-2013.pdf https://doaj.org/toc/1994-0416 https://doaj.org/toc/1994-0424 1994-0416 1994-0424 doi:10.5194/tc-7-1803-2013 https://doaj.org/article/da4c73df2dde4541a87a0d7995553213 The Cryosphere, Vol 7, Iss 6, Pp 1803-1818 (2013) Environmental sciences GE1-350 Geology QE1-996.5 article 2013 ftdoajarticles https://doi.org/10.5194/tc-7-1803-2013 2022-12-31T12:01:37Z 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 g G . Theoretical calculations show that the albedo depends on the ratio B /(1- g G ) and the asymptotic flux extinction coefficient depends on the product B (1- g G ). To understand the influence of grain shape, the values of B and g G are calculated for a variety of simple geometric shapes using ray tracing simulations. The results show that B and (1- g G ) 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 ... Article in Journal/Newspaper Antarc* Antarctica The Cryosphere Directory of Open Access Journals: DOAJ Articles The Cryosphere 7 6 1803 1818 |
institution |
Open Polar |
collection |
Directory of Open Access Journals: DOAJ Articles |
op_collection_id |
ftdoajarticles |
language |
English |
topic |
Environmental sciences GE1-350 Geology QE1-996.5 |
spellingShingle |
Environmental sciences GE1-350 Geology QE1-996.5 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 |
Environmental sciences GE1-350 Geology QE1-996.5 |
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 g G . Theoretical calculations show that the albedo depends on the ratio B /(1- g G ) and the asymptotic flux extinction coefficient depends on the product B (1- g G ). To understand the influence of grain shape, the values of B and g G are calculated for a variety of simple geometric shapes using ray tracing simulations. The results show that B and (1- g G ) 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 ... |
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 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 |
http://www.the-cryosphere.net/7/1803/2013/tc-7-1803-2013.pdf https://doaj.org/toc/1994-0416 https://doaj.org/toc/1994-0424 1994-0416 1994-0424 doi:10.5194/tc-7-1803-2013 https://doaj.org/article/da4c73df2dde4541a87a0d7995553213 |
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 |
_version_ |
1766112825788334080 |