WSL Institute for Snow and Avalanche Research SLF Davos Switzerland

Switzerland

WSL Institute for Snow and Avalanche Research SLF Davos Switzerland

Switzerland
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Kenner R.,WSL Institute for Snow and Avalanche Research SLF Davos Switzerland | Phillips M.,WSL Institute for Snow and Avalanche Research SLF Davos Switzerland | Beutel J.,ETH Zurich | Hiller M.,WSL Institute for Snow and Avalanche Research SLF Davos Switzerland | And 3 more authors.
Permafrost and Periglacial Processes | Year: 2017

This study analyses the factors controlling variations in short-term, seasonal and multiyear deformation velocity of an alpine rock glacier from data obtained over periods of 1-20 years. The Ritigraben rock glacier, in the western Swiss Alps, was monitored using tacheometry, terrestrial laser scanning, an in situ global positioning system and borehole deformation measurements. Rock glacier stratigraphy and ground temperature data were obtained from boreholes, and long-term meteorological data (temperature, precipitation, snow water equivalent) from nearby weather stations. Shearing within a distinct water-bearing layer represents the major component of the displacement. Short-term accelerations and seasonal velocity patterns of the rock glacier deformation appear to have been triggered by water supply to this layer. A long-term acceleration of the rock glacier was probably also caused by increased water supply. Permafrost temperature in the rock glacier has increased slightly since 2002, yet no direct causality could be established between this limited warming and rock glacier acceleration. © 2017 John Wiley & Sons, Ltd.


Proksch M.,University of Innsbruck | Lowe H.,WSL Institute for Snow and Avalanche Research SLF Davos Switzerland | Schneebeli M.,WSL Institute for Snow and Avalanche Research SLF Davos Switzerland
Journal of Geophysical Research F: Earth Surface | Year: 2015

Precise measurements of snow structural parameters are crucial to understand the formation of snowpacks by deposition and metamorphism and to characterize the stratigraphy for many applications and remote sensing in particular. The area-wide acquisition of structural parameters at high spatial resolution from state-of-the-art methods is, however, still cumbersome, since the time required for a single profile is a serious practical limitation. As a remedy we have developed a statistical model to extract three major snow structural parameters: density, correlation length, and specific surface area (SSA) solely from the SnowMicroPen (SMP), a high-resolution penetrometer, which allows a meter profile to be measured with millimeter resolution in less than 1 min. The model was calibrated by combining SMP data with 3-D microstructural data from microcomputed tomography which was used to reconstruct full-depth snow profiles from different snow climates (Alpine, Arctic, and Antarctic). Density, correlation length, and SSA were derived from the SMP with a mean relative error of 10.6%, 16.4%, and 23.1%, respectively. For validation, we compared the density and SSA derived from the SMP to traditional measurements and near-infrared profiles. We demonstrate the potential of our method by the retrieval of a two-dimensional stratigraphy at Kohnen Station, Antarctica, from a 46 m long SMP transect. The result clearly reveals past depositional and metamorphic events, and our findings show that the SMP can be used as an objective, high-resolution tool to retrieve essential snow structural parameters efficiently in the field. ©2015. American Geophysical Union.


Gerber F.,Ecole Polytechnique Federale de Lausanne | Lehning M.,Ecole Polytechnique Federale de Lausanne | Hoch S.W.,University of Utah | Mott R.,WSL Institute for Snow and Avalanche Research SLF Davos Switzerland
Journal of Geophysical Research: Atmospheres | Year: 2017

The rough, steep, and complex terrain in the alpine environment causes a variety of flow patterns such as blocking, speed-up, or flow separation, which influence precipitation, snow deposition, and ultimately snow distribution on the ground. Cloud-terrain interactions, flow-particle interactions, and snow transport affect snow accumulation patterns, but the relative importance of these processes is not fully understood, in particular, in complex mountainous terrain. A unique combination of measurements and model simulations is used in a local case study during a 2 day snowfall event to demonstrate the current understanding of snow accumulation in very steep alpine terrain. Doppler wind lidar measurements show an eddy-like structure on the leeward side of the Sattelhorn ridge (in the Dischma valley near Davos, Switzerland), which could partly be replicated by Advanced Regional Prediction System (ARPS) flow simulations. Snow deposition measurements with a terrestrial laser scanner show a complex deposition pattern, which is only partially captured by Alpine3D deposition simulations driven by the ARPS flow fields. This shows that additional processes such as avalanches may play a role or that a more refined simulation of flow or flow-particle interactions is required to fully understand snow distribution in very steep mountainous terrain. ©2017. American Geophysical Union.


Comola F.,Ecole Polytechnique Federale de Lausanne | Kok J.F.,University of California at Los Angeles | Gaume J.,Ecole Polytechnique Federale de Lausanne | Paterna E.,WSL Institute for Snow and Avalanche Research SLF Davos Switzerland | Lehning M.,Ecole Polytechnique Federale de Lausanne
Geophysical Research Letters | Year: 2017

Understanding the dynamics driving the transformation of snowfall crystals into blowing snow particles is critical to correctly account for the energy and mass balances in polar and alpine regions. Here we propose a fragmentation theory of fractal snow crystals that explicitly links the size distribution of blowing snow particles to that of falling snow crystals. We use discrete element modeling of the fragmentation process to support the assumptions made in our theory. By combining this fragmentation model with a statistical mechanics model of blowing snow, we are able to reproduce the characteristic features of blowing snow size distributions measured in the field and in a wind tunnel. In particular, both model and measurements show the emergence of a self-similar scaling for large particle sizes and a systematic deviation from this scaling for small particle sizes. ©2017. American Geophysical Union.


Crouzy B.,Group AHEAD | Forclaz R.,Group AHEAD | Sovilla B.,WSL Institute for Snow and Avalanche Research SLF Davos Switzerland | Corripio J.,meteoexploration.com Innsbruck Austria | Perona P.,Group AHEAD
Journal of Geophysical Research F: Earth Surface | Year: 2015

We quantify the synchronization between snowfall and natural avalanches in relation to terrain properties at the detachment zone. We analyze field statistics of 549 avalanche events in terms of slope, aspect, timing, coordinate, and release area, identified by a georeferencing procedure applied on terrestrial photography. The information from the digital pictures, together with associated meteorological data, provides us with the input needed for model calibration, namely, the magnitude of snowfall, the snow compaction rate, and the timing of precipitation and of avalanche events. Synchronization between snowfall and avalanches is established for different slope categories. We obtain an average probability of release after a snow event of 30% and 16% for the high- and low-slope categories (average slope 44° and 36°, respectively). Using the notion of information entropy, we quantify the uncertainty in predicting avalanche occurrence from a snow event. The steeper slopes correspond to a larger entropy in avalanche prediction. Further, the presented method allows us to establish the return period of avalanches without requiring a long series of data. When considering events regardless of their release depth, the avalanches had a return period of 48 days (higher slopes) and 88 days (lower slopes). Finally, we determine the average daily detachment rate as a function of snow depth and the return period of avalanches as a function of the release depth. ©2015. American Geophysical Union.


Paterna E.,WSL Institute for Snow and Avalanche Research SLF Davos Switzerland | Crivelli P.,WSL Institute for Snow and Avalanche Research SLF Davos Switzerland | Lehning M.,Ecole Polytechnique Federale de Lausanne
Geophysical Research Letters | Year: 2016

The wind-driven redistribution of snow has a significant impact on the climate and mass balance of polar and mountainous regions. Locally, it shapes the snow surface, producing dunes and sastrugi. Sediment transport has been mainly represented as a function of the wind strength, and the two processes assumed to be stationary and in equilibrium. The wind flow in the atmospheric boundary layer is unsteady and turbulent, and drifting snow may never reach equilibrium. Our question is therefore: what role do turbulent eddies play in initiating and maintaining drifting snow? To investigate the interaction between drifting snow and turbulence experimentally, we conducted several wind tunnel measurements of drifting snow over naturally deposited snow covers. We observed a coupling between snow transport and turbulent flow only in a weak saltation regime. In stronger regimes it self-organizes developing its own length scales and efficiently decoupling from the wind forcing. © 2016. American Geophysical Union. All Rights Reserved.

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