气候变化领域集成服务门户(CCPortal): Influence of grain shape on light penetration in snow

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DOI	10.5194/tc-7-1803-2013
	Influence of grain shape on light penetration in snow
	Libois Q.; Picard G.; France J.L.; Arnaud L.; Dumont M.; Carmagnola C.M.; King M.D.
发表日期	2013
ISSN	19940416
卷号	7 期号:6
英文摘要	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-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-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 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 of the data. This work highlights the large variety of snow microstructure and experimentally demonstrates that spherical grains, with B = 1.25, are inappropriate to model irradiance profiles in snow, an important result that should be considered in further studies dedicated to subsurface absorption of short-wave radiation and snow photochemistry. © Author(s) 2013. CC Attribution 3.0 License.
学科领域	albedo; energy budget; irradiance; microstructure; photochemistry; ray tracing; reflectance; shortwave radiation; snow; solar radiation; Alps; Antarctica
语种	英语
scopus关键词	albedo; energy budget; irradiance; microstructure; photochemistry; ray tracing; reflectance; shortwave radiation; snow; solar radiation; Alps; Antarctica
来源期刊	Cryosphere
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/120236
作者单位	Univ. Grenoble Alpes, LGGE (UMR5183), 38041 Grenoble, France; CNRS, LGGE (UMR5183), 38041 Grenoble, France; Department of Earth Sciences, Royal Holloway University of London, Egham, Surrey, TW20 0EX, United Kingdom; Météo-France - CNRS, CNRM - GAME UMR 3589, Centre d'Etudes de la Neige, Grenoble, France
推荐引用方式 GB/T 7714	Libois Q.,Picard G.,France J.L.,et al. Influence of grain shape on light penetration in snow[J],2013,7(6).
APA	Libois Q..,Picard G..,France J.L..,Arnaud L..,Dumont M..,...&King M.D..(2013).Influence of grain shape on light penetration in snow.Cryosphere,7(6).
MLA	Libois Q.,et al."Influence of grain shape on light penetration in snow".Cryosphere 7.6(2013).