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| Titel |
Impacts of light-absorbing impurities on snow and their quantification with bidirectional reflectance measurements |
| VerfasserIn |
Maria Gritsevich, Jouni Peltoniemi, Outi Meinander, Pavla Dagsson-Waldhauserová, Nataliya Zubko, Teemu Hakala, Aki Virkkula, Jonas Svensson, Gerrit de Leeuw |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250153607
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| Publikation (Nr.) |
 EGU/EGU2017-18605.pdf |
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| Zusammenfassung |
| In order to quantify the effects of absorbing impurities on snow and define their contribution to the climate
change, we have conducted a series of dedicated bidirectional reflectance measurements. Chimney soot, volcanic
sand, and glaciogenic silt have been deposited on the snow in the controlled way. The bidirectional reflectance
factors of these targets and untouched snow have been measured using the Finnish Geodetic Institute’s field
goniospectrometer FIGIFIGO, see, e.g., [1, 2] and references therein. It has been found that the contaminants
darken the snow, and modify its appearance mostly as expected, with clear directional signal and modest spectral
signal. A remarkable feature is the fact that any absorbing contaminant on snow enhances the metamorphosis
under strong sunlight [3, 4]. Immediately after deposition, the contaminated snow surface appears darker than
the pure snow in all viewing directions, but the heated soot particles start sinking down deeply into the snow in
minutes. The nadir measurement remains darkest, but at larger zenith angles the surface of the soot-contaminated
snow changes back to almost as white as clean snow. Thus, for on ground observer the darkening by impurities
can be completely invisible, overestimating the albedo, but a nadir looking satellite sees the darkest points, now
underestimating the albedo.
After more time, also the nadir view brightens, and the remaining impurities may be biased towards more
shadowed locations or less absorbing orientations by natural selection. This suggests that at noon the albedo
should be lower than in the morning or afternoon. When sunlight stimulates more sinking than melting, albedo
should be higher in the afternoon than in the morning, and vice versa when melting is dominating. Thus to
estimate the effects caused by black carbon (BC) deposited on snow on climate changes may one need to take
into account possible rapid diffusion of the BC inside the snow from its surface. When the snow melt rate
gets faster than the diffusion rate (under condition of warm outside temperatures), as it was observed at the
end of the experiment reported here, dark material starts accumulating into the surface [5]. The BC deposited
on snow at warm temperatures initiates rapid melting process and may cause dramatic changes on the snow surface.
References
1 Peltoniemi J.I., Hakala T., Suomalainen J., Honkavaara E., Markelin L., Gritsevich M., Eskelinen J., Jaanson
P., Ikonen E. (2014): Technical notes: A detailed study for the provision of measurement uncertainty and
traceability for goniospectrometers. Journal of Quantitative Spectroscopy & Radiative Transfer 146, 376-390,
http://dx.doi.org/10.1016/j.jqsrt.2014.04.011
2 Zubko N., Gritsevich M., Zubko E., Hakala T., Peltoniemi J.I. (2016): Optical measurements of chemically
heterogeneous particulate surfaces // Journal of Quantitative Spectroscopy and Radiative Transfer, 178, 422-431,
http://dx.doi.org/10.1016/j.jqsrt.2015.12.010
3 Peltoniemi J.I., Gritsevich M., Hakala T., Dagsson-Waldhauserová P., Arnalds Ó., Anttila K., Hannula H.-R.,
Kivekäs N., Lihavainen H., Meinander O., Svensson J., Virkkula A., de Leeuw G. (2015): Soot on snow exper-
iment: bidirectional reflectance factor measurements of contaminated snow // The Cryosphere, 9, 2323–2337,
http://dx.doi.org/10.5194/tc-9-2323-2015
4 Svensson J., Virkkula A., Meinander O., Kivekäs N., Hannula H.-R., Järvinen O., Peltoniemi J.I., Gritsevich M.,
Heikkilä A., Kontu A., Neitola K., Brus D., Dagsson-Waldhauserova P., Anttila K., Vehkamäki M., Hienola A.,
de Leeuw G. & Lihavainen H. (2016): Soot-doped natural snow and its albedo — results from field experiments.
Boreal Environment Research, 21, 481–503, http://www.borenv.net/BER/pdfs/preprints/Svensson1498.pdf
5 Meinander O., Kontu A., Virkkula A., Arola A., Backman L., Dagsson-Waldhauserová P., Järvinen O., Manninen
T., Svensson J., de Leeuw G., and Leppäranta M. (2014): Brief communication: Light-absorbing impurities can
reduce the density of melting snow, The Cryosphere, 8, 991-995, doi:10.5194/tc-8-991-2014. |
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