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| Titel |
Mineral dust radiative effect on snow in European Alps |
| VerfasserIn |
Biagio Di Mauro, Francesco Fava, Luca Ferrero, Roberto Garzonio, Giovanni Baccolo, Barbara Delmonte, Roberto Colombo |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250103994
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| Publikation (Nr.) |
 EGU/EGU2015-3416.pdf |
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| Zusammenfassung |
| Mineral Dust (MD) is known to increase the absorption of solar radiation when deposited on
snow and ice. This process causes a decrease in the albedo and may enhance snow melting,
resulting in a positive radiative forcing (RF) in climate system. The RF from MD on snow
can assume high values (~100-200 W/m2) after depositional events altering snow and ice
radiative balance and hydrological cycle.
In this study, we analyzed a significant MD transport happened during spring in 2014 and
in particular its impact on snow optical properties. The dust plume was entrained in the
troposphere over the Saharan desert (North African Grand Erg Oriental) during the
passage of a cold front, and then transported NE over the Mediterranean by cyclonic
atmospheric conditions. MD reached the European Alps where it was deposited by
snowfall. We conducted a field proximal sensing survey in 10 plots (2x2 meters) at the
Artavaggio plains (Lecco, Italy) with a hyperspectral radiometer (ASD Field-spec pro)
collecting reflected radiance of snow in a spectral range between 350 and 2500 nm.
Surface snow samples were collected and analyzed in clean room with microparticle
counter in order to determine the size distribution and the concentration of MD in
each sample. In addition, total mass of insoluble material was also measured by
filtering the melted snow. Observed spectra were compared to those simulated by
parameterizing the Snow, Ice, and Aerosol Radiation (SNICAR) radiative transfer model
with observed variables such as snow grain size, snow density and size distribution
of MD. We defined a novel spectral index, the Snow Darkening Index (SDI) to
combine red and green wavelengths showing nonlinear correlation with measured MD
concentration. Instantaneous radiative forcing was then estimated as the spectral
difference between upwelling irradiance of plot containing MD and pure snow
plots. MD concentration was up to 107 ppm and total mass of insoluble material up
to 325 ppm. Measured RF values reached 153 W/m2 in the highest concentrated
plot.
During the survey, an overflight of a four-rotors Unmanned Aerial Vehicle (UAV)
equipped with an RGB digital camera sensor was organized. Data from UAV were analysed
in order to produce a high resolution Digital Surface Model and an orthomosaic image of the
area. Furthermore, RBG channels were combined to produce a detailed SDI map of the study
area. Finally, a Landsat 8 Operational Land Imager (OLI) tile was atmospherically and
topographically corrected and maps of SDI in central European Alps were calculated from
red and green reflectances. MD in snow showed high spatial variability with higher
concentration in South facing slopes. These results represent the first evidence that aeolian
transported MD from desert region can strongly influence snow and ice radiative balance in
European Alps. |
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