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The Cryosphere An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/tc-2018-255
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2018-255
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 05 Dec 2018

Research article | 05 Dec 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal The Cryosphere (TC).

Avalanches and micrometeorology driving mass and energy balance of the lowest perennial ice field of the Alps: a case study

Rebecca Mott1,2, Andreas Wolf3, Maximilian Kehl1, Harald Kunstmann1,4, Michael Warscher1,4,5, and Thomas Grünewald2 Rebecca Mott et al.
  • 1Institute of Meteorology and Climate Research, Atmospheric Environmental Research (KIT/IMK-IFU), KIT-Campus Alpin, Garmisch-Partenkirchen, Germany
  • 2WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland
  • 3Institute for Karst and Cave Science, Germany
  • 4Institute of Geography, University of Augsburg
  • 5Department of Geography, University of Innsbruck, Austria

Abstract. The mass balance of very small glaciers is often governed either by anomalous snow accumulation, winter precipitation being multiplied by snow redistribution processes (gravitationally or wind-driven), or by suppressed snow ablation driven by micrometeorological effects lowering net radiation and/or turbulent heat exchange. In this case study, we analysed the relative contribution of snow accumulation and ablation processes governing the long- and short-term mass balance of the lowest perennial ice field of the Alps, the Ice Chapel, located at 870m ASL in the Berchtesgaden National Park (Germany). This study emphasizes the importance of the local topographic setting for the survival of a perennial ice field located far below the climatic snow line. Although long-term mass balance measurements of the ice field surface showed a dramatic mass loss between 1973 and 2014, the ice field mass balance was rather stable between 2014 and 2017 and even showed a strong mass gain in 2017/2018 with an increase in surface height by 50–100% relative to the ice field thickness. Measurements suggest that the winter mass balance clearly dominated the annual mass balance with 3000% of winter snow accumulation compared to a near-by flat field station. At the Ice Chapel surface, 92% of snow accumulation was gained by snow avalanching, thus clearly governing the 2017/2018 winter mass balance of the ice field with mean snow depths of 32m at the end of the accumulation period. Avalanche deposition was amplified by preferential deposition of snowfall in the wind-sheltered rock face surrounding the ice field.

Detailed micrometeorological measurements combined with a numerical analysis of the small-scale near-surface atmospheric flow field identified the micrometeorological processes driving the energy balance of the ice field. Measurements revealed a katabatic flow system draining down the ice field throughout the day, showing strong temporal and spatial dynamics. The spatial origin of the onset of the thermal flow system, was shown to be of particular importance for the ice field surface energy balance. Deep katabatic flows, that developed at higher-elevated shaded areas of the rock face and drained down the ice field appeared to enhance sensible heat exchange towards the ice field surface by enhancing turbulence close to the ice surface. Contrary, the shallow katabatic flow developing at the ice field surface appeared to laterally decouple the local near-surface atmosphere from the warmer adjacent air supressing heat exchange. Results thus suggest that shallow katabatic flows driven by the cooling effect of the ice field surface are especially efficient in lowering the climatic sensitivity of the ice field to the surrounding rising air temperatures. Such micrometeorological phenomena must be taken into account when calculating mass and energy balances of very small glaciers or perennial ice fields at elevations far below the climatic snow line.

Rebecca Mott et al.
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Short summary
The mass balance of very small glaciers is often governed either by anomalous snow accumulation, winter precipitation being multiplied by snow redistribution processes, or by suppressed snow ablation driven by micrometeorological effects lowering net radiation and turbulent heat exchange. In this study we discuss the relative contribution of snow accumulation (avalanches) versus micrometeorlogy (katabatic flow) on the mass balance of the lowest perrennial ice field of the Alps, the Ice Chapel.
The mass balance of very small glaciers is often governed either by anomalous snow accumulation,...
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