Brief communication: Light-absorbing impurities can reduce the density of melting snow

Meinander, Outi; Kontu, Anna; Virkkula, Aki; Arola, Antti; Backman, Leif; Dagsson-Waldhauserová, Pavla; Järvinen, Onni; Manninen, Terhikki; Svensson, Jonas; Leeuw, Gerrit de; Leppäranta, Matti

doi:10.5194/tc-8-991-2014

Cited by 40 publications

(43 citation statements)

References 10 publications

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“…Although the change in grain size is on the order of the uncertainty in grain size retrieval, it is not the absolute values that are important but rather the trend. A decrease in surface grain size in the presence of high impurity content was also observed in the daily field observations in 2013 by Skiles (2014), when the dust layers coalesced at the surface and skies were clear both grain sizes and density in the surface layers decreased and surface roughness increased, consistent with observations in other regions (Meinander et al, 2014). Skiles (2014) and Painter et al (2013) as well as the results in this paper suggest that the intensification of snowmelt by dust in the visible wavelengths results in destructive metamorphism near the snow-atmosphere interface and snowmelt infiltration with refreezing and snow grain coarsening at depths of approximately 2 to 10 cm.…”

Section: Uncertainty and Error Analysissupporting

confidence: 76%

“…Besides snowmelt, snowfall impacts snowpack properties very rapidly and, thus, it is important to capture temporal changes in addition to spatial patterns. For example, Molotch et al (2004) showed that spatially distributed snowmelt models benefit significantly from incorporating snow albedo estimates derived from the NASA/JPL Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data instead of using empirical basin-wide snow albedo assumptions.…”

Section: Introductionmentioning

confidence: 99%

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Case study of spatial and temporal variability of snow cover, grain size, albedo and radiative forcing in the Sierra Nevada and Rocky Mountain snowpack derived from imaging spectroscopy

et al. 2016

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Abstract. Quantifying the spatial distribution and temporal change in mountain snow cover, microphysical and optical properties is important to improve our understanding of the local energy balance and the related snowmelt and hydrological processes. In this paper, we analyze changes of snow cover, optical-equivalent snow grain size (radius), snow albedo and radiative forcing by light-absorbing impurities in snow and ice (LAISI) with respect to terrain elevation and aspect at multiple dates during the snowmelt period. These snow properties are derived from the NASA/JPL Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data from 2009 in California's Sierra Nevada and from 2011 in Colorado's Rocky Mountains, USA.Our results show a linearly decreasing snow cover during the ablation period in May and June in the Rocky Mountains and a snowfall-driven change in snow cover in the Sierra Nevada between February and May. At the same time, the snow grain size is increasing primarily at higher elevations and north-facing slopes from 200 microns to 800 microns on average. We find that intense snowmelt renders the mean grain size almost invariant with respect to elevation and aspect. Our results confirm the inverse relationship between snow albedo and grain size, as well as between snow albedo and radiative forcing by LAISI. At both study sites, the mean snow albedo value decreases from approximately 0.7 to 0.5 during the ablation period. The mean snow grain size increased from approximately 150 to 650 microns. The mean radiative forcing increases from 20 W m −2 up to 200 W m −2 during the ablation period. The variability of snow albedo and grain size decreases in general with the progression of the ablation period. The spatial variability of the snow albedo and grain size decreases through the melt season while the spatial variability of radiative forcing remains constant.

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Section: Uncertainty and Error Analysissupporting

confidence: 76%

Section: Introductionmentioning

confidence: 99%

Case study of spatial and temporal variability of snow cover, grain size, albedo and radiative forcing in the Sierra Nevada and Rocky Mountain snowpack derived from imaging spectroscopy

et al. 2016

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“…However, different melting conditions, or different hydrophobic properties of the contaminants, may reverse the process, accumulating the dirt on the surface (Conway et al, 1996;Meinander et al, 2014). Such snow was not measured…”

Section: Discussionmentioning

confidence: 99%

“…Experiments were conducted in different regions in Finland, in 2011 and, with the general aim to monitor and quantify the effects of soot on the albedo and physical properties of the snowpack. To this end, absorbing aerosols of different origins were deposited on a natural snowpack in a controlled way and the changes in the snowpack properties were measured (Meinander et al, 2014;Svensson et al, 2015). In this Figure 1.…”

Section: J I Peltoniemi Et Al: Reflectance Of Contaminated Snowmentioning

confidence: 99%

“…The Finnish Meteorological Institute (FMI) organized a series of experiments, using a different approach than the cited studies (Meinander et al, 2014;Svensson et al, 2015). Experiments were conducted in different regions in Finland, in 2011 and, with the general aim to monitor and quantify the effects of soot on the albedo and physical properties of the snowpack.…”

Section: J I Peltoniemi Et Al: Reflectance Of Contaminated Snowmentioning

confidence: 99%

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Soot on Snow experiment: bidirectional reflectance factor measurements of contaminated snow

et al. 2015

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Abstract. In order to quantify the effects of absorbing contaminants on snow, a series of spectral reflectance measurements were conducted. Chimney soot, volcanic sand, and glaciogenic silt were deposited on a natural snow surface in a controlled way as a part of the Soot on Snow (SoS) campaign. The bidirectional reflectance factors of these soiled surfaces and untouched snow were measured using the Finnish Geodetic Institute's Field Goniospectropolariradiometer, FIGIFIGO.A remarkable feature is the fact that the absorbing contaminants on snow enhanced the metamorphism of snow under strong sunlight in our experiments. Immediately after deposition, the contaminated snow surface appeared darker than the natural snow in all viewing directions, but the absorbing particles sank deep into the snow in minutes. The nadir measurement remained the darkest, but at larger zenith angles, the surface of the contaminated snow changed back to almost as white as clean snow. Thus, for a ground observer the darkening caused by impurities can be completely invisible, overestimating the albedo, but a nadir-observing satellite sees the darkest points, underestimating the albedo. Through a reciprocity argument, we predict that at noon, the albedo perturbation should be lower than in the morning or afternoon. When sunlight stimulates sinking more than melting, the albedo should be higher in the afternoon than in the morning, and vice versa when melting dominates. However, differences in the hydrophobic properties, porosity, clumping, or size of the impurities may cause different results than observed in these measurements.

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Mineral dust impact on snow radiative properties in the European Alps combining ground, UAV, and satellite observations

et al. 2015

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In this paper, we evaluate the impact of mineral dust (MD) on snow radiative properties in the European Alps at ground, aerial, and satellite scale. A field survey was conducted to acquire snow spectral reflectance measurements with an Analytical Spectral Device (ASD) Field Spec Pro spectroradiometer. Surface snow samples were analyzed to determine the concentration and size distribution of MD in each sample. An overflight of a four-rotor Unmanned Aerial Vehicle (UAV) equipped with an RGB digital camera sensor was carried out during the field operations. Finally, Landsat 8 Operational Land Imager (OLI) data covering the central European Alps were analyzed. Observed reflectance evidenced that MD strongly reduced the spectral reflectance of snow, in particular, from 350 to 600 nm. Reflectance was compared with that simulated by parameterizing the Snow, Ice, and Aerosol Radiation radiative transfer model. We defined a novel spectral index, the Snow Darkening Index (SDI), that combines different wavelengths showing nonlinear correlation with measured MD concentrations (R 2 = 0.87, root-mean-square error = 0.037). We also estimated a positive instantaneous radiative forcing that reaches values up to 153 W/m 2 for the most concentrated sampling area. SDI maps at local scale were produced using the UAV data, while regional SDI maps were generated with OLI data. These maps show the spatial distribution of MD in snow after a natural deposition from the Saharan desert. Such postdepositional experimental data are fundamental for validating radiative transfer models and global climate models that simulate the impact of MD on snow radiative properties.

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Brief communication: Light-absorbing impurities can reduce the density of melting snow

Cited by 40 publications

References 10 publications

Case study of spatial and temporal variability of snow cover, grain size, albedo and radiative forcing in the Sierra Nevada and Rocky Mountain snowpack derived from imaging spectroscopy

Case study of spatial and temporal variability of snow cover, grain size, albedo and radiative forcing in the Sierra Nevada and Rocky Mountain snowpack derived from imaging spectroscopy

Soot on Snow experiment: bidirectional reflectance factor measurements of contaminated snow

Mineral dust impact on snow radiative properties in the European Alps combining ground, UAV, and satellite observations

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