Evolution of the Surface Area of a Snow Layer

Hanot, Laurence; Dominé, Florent

doi:10.1021/es9811288

Cited by 53 publications

(47 citation statements)

References 28 publications

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“…The sampling procedure has been described earlier (Hanot and Domine, 1999). Briefly, a new snow pit with vertical faces was dug for each sampling to observe the stratigraphy and identify the layers of interest.…”

Section: Snow Samplingmentioning

confidence: 99%

Acetaldehyde in the Alaskan subarctic snowpack

et al. 2010

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Abstract. Acetaldehyde is a reactive intermediate in hydrocarbon oxidation. It is both emitted and taken up by snowpacks and photochemical and physical processes are probably involved. Understanding the reactivity of acetaldehyde in snow and its processes of physical and chemical exchanges requires the knowledge of its incorporation mechanism in snow crystals. We have performed a season-long study of the evolution of acetaldehyde concentrations in the subarctic snowpack near Fairbanks (65 • N), central Alaska, which is subjected to a vigorous metamorphism due to persistent elevated temperature gradients in the snowpack, between 20 and 200 • C m −1 . The snowpack therefore almost entirely transforms into depth hoar. We have also analyzed acetaldehyde in a manipulated snowpack where temperature gradients were suppressed. Snow crystals there transformed much more slowly and their original shapes remained recognizable for months. The specific surface area of snow layers in both types of snowpacks was also measured. We deduce that acetaldehyde is not adsorbed onto the surface of snow crystals and that most of the acetaldehyde is probably not dissolved in the ice lattice of the snow crystals. We propose that most of the acetaldehyde measured is either trapped or dissolved within organic aerosol particles trapped in snow, or that acetaldehyde is formed by the hydrolysis of organic precursors contained in organic aerosols trapped in the snow, when the snow is melted for analysis. These precursors are probably aldehyde polymers formed within the aerosol particles by Correspondence to: F. Domine (florent@lgge.obs.ujf-grenoble.fr) acid catalysis, but might also be biological molecules. In a laboratory experiment, acetaldehyde-di-n-hexyl acetal, representing a potential acetaldehyde precursor, was subjected to our analytical procedure and reacted to form acetaldehyde. This confirms our suggestion that acetaldehyde detected in snow could be produced during the melting of snow for analysis.

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Section: Snow Samplingmentioning

confidence: 99%

Acetaldehyde in the Alaskan subarctic snowpack

et al. 2010

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“…The sampling procedure employed in this study has been described earlier (Hanot andDomine, 1999 andDomine et al, 2002). Briefly, a new snow pit with vertical faces was excavated for each sampling event to observe the stratigraphy and identify the layers of interest.…”

Section: Snow Samplingmentioning

confidence: 99%

Three examples where the specific surface area of snow increased over time

et al. 2009

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Abstract. Snow on the ground impacts climate through its high albedo and affects atmospheric composition through its ability to adsorb chemical compounds. The quantification of these effects requires the knowledge of the specific surface area (SSA) of snow and its rate of change. All relevant studies indicate that snow SSA decreases over time. Here, we report for the first time three cases where the SSA of snow increased over time. These are (1) the transformation of a melt-freeze crust into depth hoar, producing an increase in SSA from 3.4 to 8.8 m 2 kg −1 . (2) The mobilization of surface snow by wind, which reduced the size of snow crystals by sublimation and fragmented them. This formed a surface snow layer with a SSA of 61 m 2 kg −1 from layers whose SSAs were originally 42 and 50 m 2 kg −1 . (3) The sieving of blowing snow by a snow layer, which allowed the smallest crystals to penetrate into open spaces in the snow, leading to an SSA increase from 32 to 61 m 2 kg −1 . We discuss that other mechanisms for SSA increase are possible. Overall, SSA increases are probably not rare. They lead to enhanced uptake of chemical compounds and to increases in snow albedo, and their inclusion in relevant chemical and climate models deserves consideration.

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“…The first situation leads to the formation of hexagonal crystals, often hollow and cup-shaped, called depth hoar crystals. The second situation leads to the formation of faceted surface hoar crystals, but their shapes show more variation and include hollow cups and feather-shaped crystals Hachikubo and Akitaya, 1997;Hanot and Dominé, 1999;Legagneux et al, 2002). Both depth hoar and surface hoar crystals grow to large sizes, sometimes several cm, that have little cohesion and form snow layers of high permeability.…”

Section: Dry Metamorphism Of Snowmentioning

confidence: 99%

Snow metamorphism as revealed by scanning electron microscopy

Dominé

Lauzier

Cabanes

et al. 2003

Microscopy Res & Technique

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Current theories of snow metamorphism indicate that sublimating snow crystals have rounded shapes, while growing crystals have shapes that depend on growth rates. At slow growth rates, crystals are rounded. At moderate rates, they have flat faces with rounded edges. At fast growth rates, crystals have flat faces with sharp edges, and they have hollow faces at very fast growth rates. The main growth/sublimation mechanism is thought to be by the homogeneous nucleation of new layers at or near crystal edges. It was also suggested that the equilibrium shape of snow crystals would be temperature dependent: rounded above -10.5 degrees C, and faceted below. To test these paradigms, we have performed SEM investigations of snow samples having undergone metamorphism under natural conditions, and of snow samples subjected to isothermal metamorphism at -4 degrees and -15 degrees C in the laboratory. In general, current theories predicting crystal shapes as a function of growth rates, and of whether crystals are growing or sublimating, are verified. However, the transition in equilibrium shapes from rounded to faceted at -10.5 degrees C is not observed in our isothermal experiments that reveal a predominance of rounded shapes after more than a month of metamorphism at -4 and -15 degrees C. Some small crystals with flat faces that also have sharp angles at -15 degrees C, are observed in our isothermal experiments. These faces are newly formed, and contradict current theory. Several hypotheses are proposed to explain their occurrence. One is that they are due to sublimation at emerging dislocations.

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Evolution of the Surface Area of a Snow Layer

Cited by 53 publications

References 28 publications

Acetaldehyde in the Alaskan subarctic snowpack

Acetaldehyde in the Alaskan subarctic snowpack

Three examples where the specific surface area of snow increased over time

Snow metamorphism as revealed by scanning electron microscopy

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