The growth of sublimation crystals and surface hoar on the Antarctic plateau

Gallet, Jean‐Charles; Dominé, Florent; Savarino, Joël; Dumont, Marie; Brun, E.

doi:10.5194/tc-8-1205-2014

Cited by 45 publications

(52 citation statements)

References 44 publications

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“…The difference in optical effective particle radius between different wavelengths was largest on 5 and 6 January, when strong melting occurred and large, irregular surface snow particles with thin protrusions coexisted with smaller particles (see Table 3), causing a rough texture in the millimetre scale. This seems to be a rather common feature of the Antarctic snow surface, also observed on the high plateau (Gallet et al, 2014). At the shortest SWIR wavelengths, photons can penetrate several millimetres into the snowpack (see Fig.…”

Section: Model Discrepanciesmentioning

confidence: 99%

Measurements and modelling of snow particle size and shortwave infrared albedo over a melting Antarctic ice sheet

et al. 2015

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Abstract. The albedo of a snowpack depends on the singlescattering properties of individual snow crystals, which have a variety of shapes and sizes, and are often bounded in clusters. From the point of view of optical modelling, it is essential to identify the geometric dimensions of the population of snow particles that synthesize the scattering properties of the snowpack surface. This involves challenges related to the complexity of modelling the radiative transfer in such an irregular medium, and to the difficulty of measuring microphysical snow properties. In this paper, we illustrate a method to measure the size distribution of a snow particle parameter, which roughly corresponds to the smallest snow particle dimension, from two-dimensional macro photos of snow particles taken in Antarctica at the surface layer of a melting ice sheet. We demonstrate that this snow particle metric corresponds well to the optically equivalent effective radius utilized in radiative transfer modelling, in particular when snow particles are modelled with the droxtal shape. The surface albedo modelled on the basis of the measured snow particle metric showed an excellent match with the observed albedo when there was fresh or drifted snow at the surface. In the other cases, a good match was present only for wavelengths longer than 1.4 µm. For shorter wavelengths, our modelled albedo generally overestimated the observations, in particular when surface hoar and faceted polycrystals were present at the surface and surface roughness was increased by millimetre-scale cavities generated during melting. Our results indicate that more than just one particle metric distribution is needed to characterize the snow scattering properties at all optical wavelengths, and suggest an impact of millimetre-scale surface roughness on the shortwave infrared albedo.

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Section: Model Discrepanciesmentioning

confidence: 99%

Measurements and modelling of snow particle size and shortwave infrared albedo over a melting Antarctic ice sheet

et al. 2015

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“…The SSA variations observed by CORAS on 24 December 2013 are of the same order of magnitude. However, the variations observed by Gallet et al (2014b) are not symmetric to noon and their sign changes on a day-to-day scale due to the strong dependence on meteorological conditions. Even though an influence of crystal growth processes cannot be ruled out for the measurements presented here, the evident dependence on the solar zenith angle and the constant symmetry to noon of the diurnal cycle observed in the SSA retrieved from CORAS measurements strongly indicate a dominating influence of the solar zenith angle.…”

Section: Application In Cloudless Conditionsmentioning

confidence: 99%

“…To derive a more general description of the escape function, more cases and explicit BRDF measurements are needed, which is beyond the scope of this study. Furthermore, Gallet et al (2014b) observed SSA variations on a sub-daily scale using the DUFISSS instrument (DUal Frequency Integrating Sphere for Snow SSA measurements; Gallet et al, 2009) at Dome C in January 2009. They measured a drop in SSA at around noon from 40 to 33 m 2 kg −1 before the SSA increased again to 41 m 2 kg −1 at midnight.…”

Section: Application In Cloudless Conditionsmentioning

confidence: 99%

Comparison of different methods to retrieve optical-equivalent snow grain size in central Antarctica

et al. 2017

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Abstract. The optical-equivalent snow grain size affects the reflectivity of snow surfaces and, thus, the local surface energy budget in particular in polar regions. Therefore, the specific surface area (SSA), from which the optical snow grain size is derived, was observed for a 2-month period in central Antarctica (Kohnen research station) during austral summer 2013/14. The data were retrieved on the basis of ground-based spectral surface albedo measurements collected by the COmpact RAdiation measurement System (CORAS) and airborne observations with the Spectral Modular Airborne Radiation measurement sysTem (SMART). The snow grain size and pollution amount (SGSP) algorithm, originally developed to analyze spaceborne reflectance measurements by the MODerate Resolution Imaging Spectroradiometer (MODIS), was modified in order to reduce the impact of the solar zenith angle on the retrieval results and to cover measurements in overcast conditions. Spectral ratios of surface albedo at 1280 and 1100 nm wavelength were used to reduce the retrieval uncertainty. The retrieval was applied to the ground-based and airborne observations and validated against optical in situ observations of SSA utilizing an IceCube device. The SSA retrieved from CORAS observations varied between 27 and 89 m 2 kg −1 . Snowfall events caused distinct relative maxima of the SSA which were followed by a gradual decrease in SSA due to snow metamorphism and wind-induced transport of freshly fallen ice crystals. The ability of the modified algorithm to include measurements in overcast conditions improved the data coverage, in particular at times when precipitation events occurred and the SSA changed quickly. SSA retrieved from measurements with CORAS and MODIS agree with the in situ observations within the ranges given by the measurement uncertainties. However, SSA retrieved from the airborne SMART data slightly underestimated the ground-based results.

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“…This leads to a maximum Pe ≈ 0.8; (3) Pe > 1 would be possible for depth hoar (Alley et al, 1990) or kinetic growth crystals, like sublimation crystals (Gallet et al, 2014, Adams andWalter, 2014) close to the surface but they were only formed under light winds conditions. According to the reported Beaufort number (in Alley et al, 1990), this will be a maximum wind speed of ≈ 2-3 m s −1 (see also Gallet et al, 2014) above the surface. In addition, they were developed in the slopes of older dunes, leading to an additional decrease of the actual wind speed (≈ 1 m s −1 ) above the layers.…”

Section: Methodsmentioning

confidence: 99%

Tomography-based monitoring of isothermal snow metamorphism under advective conditions

Ebner

Schneebeli²,

Steinfeld

2015

The Cryosphere

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Abstract. Time-lapse X-ray microtomography was used to investigate the structural dynamics of isothermal snow metamorphism exposed to an advective airflow. The effect of diffusion and advection across the snow pores on the snow microstructure were analysed in controlled laboratory experiments and possible effects on natural snowpacks discussed. The 3-D digital geometry obtained by tomographic scans was used in direct pore-level numerical simulations to determine the effective permeability. The results showed that isothermal advection with saturated air have no influence on the coarsening rate that is typical for isothermal snow metamorphism. Isothermal snow metamorphism is driven by sublimation deposition caused by the Kelvin effect and is the limiting factor independently of the transport regime in the pores.

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The growth of sublimation crystals and surface hoar on the Antarctic plateau

Cited by 45 publications

References 44 publications

Measurements and modelling of snow particle size and shortwave infrared albedo over a melting Antarctic ice sheet

Measurements and modelling of snow particle size and shortwave infrared albedo over a melting Antarctic ice sheet

Comparison of different methods to retrieve optical-equivalent snow grain size in central Antarctica

Tomography-based monitoring of isothermal snow metamorphism under advective conditions

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