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| Titel |
Micrometeorological processes driving snow ablation in an Alpine catchment |
| VerfasserIn |
R. Mott, L. Egli, T. Grünewald, N. Dawes, C. Manes, M. Bavay, M. Lehning |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1994-0416
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| Digitales Dokument |
URL |
| Erschienen |
In: The Cryosphere ; 5, no. 4 ; Nr. 5, no. 4 (2011-11-30), S.1083-1098 |
| Datensatznummer |
250002760
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| Publikation (Nr.) |
 copernicus.org/tc-5-1083-2011.pdf |
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| Zusammenfassung |
| Mountain snow covers typically become patchy over the course of a melting
season. The snow pattern during melt is mainly governed by the end of winter
snow depth distribution and the local energy balance. The objective of this
study is to investigate micro-meteorological processes driving snow ablation
in an Alpine catchment. For this purpose we combine a meteorological
boundary-layer model (Advanced Regional Prediction System) with a fully
distributed energy balance model (Alpine3D). Turbulent fluxes above melting
snow are further investigated by using data from eddy-correlation systems. We
compare modeled snow ablation to measured ablation rates as obtained from a
series of Terrestrial Laser Scanning campaigns covering a complete ablation
season. The measured ablation rates indicate that the advection of sensible
heat causes locally increased ablation rates at the upwind edges of the snow
patches. The effect, however, appears to be active over rather short
distances of about 4–6 m. Measurements suggest that mean wind velocities of
about 5 m s−1 are required for advective heat transport to increase
snow ablation over a long fetch distance of about 20 m. Neglecting this
effect, the model is able to capture the mean ablation rates for early
ablation periods but strongly overestimates snow ablation once the fraction
of snow coverage is below a critical value of approximately 0.6. While
radiation dominates snow ablation early in the season, the turbulent flux
contribution becomes important late in the season. Simulation results
indicate that the air temperatures appear to overestimate the local air
temperature above snow patches once the snow coverage is low. Measured turbulent
fluxes support these findings by suggesting a stable internal boundary layer
close to the snow surface causing a strong decrease of the sensible heat flux
towards the snow cover. Thus, the existence of a stable internal boundary
layer above a patchy snow cover exerts a dominant control on the timing and
magnitude of snow ablation for patchy snow covers. |
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