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| Titel |
Orographic effects on snow-deposition patterns in mountainous terrain |
| VerfasserIn |
Rebecca Mott, Danny Scipion, Marc Schneebeli, Nicholas Dawes, Alexis Berne, Michael Lehning |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250095061
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| Publikation (Nr.) |
 EGU/EGU2014-10501.pdf |
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| Zusammenfassung |
| The interaction of moist air flow with topography causes the modification of rain, snow and other hydrometeors, also known as orographic precipitation. In this study, we present a multi-scale discussion on processes driving the local enhancement/depletion of snowfall and snow deposition at the ground for one heavy snowfall event in March 2011. We combine a discussion on the evolution of frontal processes with the analysis of smaller-scale effects of the seeder-feeder mechanism, mountain wave propagation, and flow-particle interactions. For this purpose, a polarimetric X-band radar was deployed in the area of Davos (Switzerland) to measure snowflake concentration fields in the atmosphere. The evolution of frontal processes was examined by analysing modelled precipitation fields obtained from COSMO-2 and measured profiles of the atmosphere and radial velocities. In order to identify smaller scale processes, we related measured precipitation fields to flow dynamics by modeling small-scale flow fields (horizontal resolution of 25 m) with the atmospheric model `Advanced Regional Prediction System (ARPS)'. Additionally, we modelled snow accumulation at the surface with Alpine3D and compared snow deposition fields with snowflake concentration fields measured by the radar. Furthermore, microphysical processes were discussed by analyzing the horizontal and vertical distribution of polarimetric radar variables. At larger scales, enhanced precipitation rates were found to be a result of the evolution of a shear layer that accompanied the passage of the frontal system. At smaller scales, the radar data revealed polarimetric signatures of orographic snowfall enhancement near the summit region. Increased radar reflectivity at horizontal polarization was observed over the windward slopes towards the crest and the downwind decreasing reflectivity over the leeward slopes. We could detect a variation in the location of maximum concentration of snow particles, that was partly attributed to the effect of the local flow field: Strong horizontal winds caused a shift of the concentration maximum from the ridge crest towards the leeward slopes. Furthermore, we discussed the relative role of cloud microphysics such as the seeder-feeder mechanism versus atmospheric particle transport in generating the observed snow deposition at the ground. We were able to present arguments that two processes dominated the snowfall and snow deposition fields observed in this study: 1. Sufficiently strong updrafts induced local feeder clouds above the summits promoting enhanced snow deposition. 2. Pure particle-flow interaction named preferential deposition was active in all cases of sufficient wind, but produced a smaller differentiation in snow deposition. |
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