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Volume 10, issue 1
The Cryosphere, 10, 445-458, 2016
https://doi.org/10.5194/tc-10-445-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
The Cryosphere, 10, 445-458, 2016
https://doi.org/10.5194/tc-10-445-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 29 Feb 2016

Research article | 29 Feb 2016

Wind tunnel experiments: cold-air pooling and atmospheric decoupling above a melting snow patch

Rebecca Mott1, Enrico Paterna1, Stefan Horender1, Philip Crivelli1, and Michael Lehning1,2 Rebecca Mott et al.
  • 1WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland
  • 2School of Architecture, Civil and Environmental Engineering, Laboratory of Cryospheric Sciences (CRYOS), Ècole Polytechnique Fèdèrale de Lausanne, Lausanne, Switzerland

Abstract. The longevity of perennial snowfields is not fully understood, but it is known that strong atmospheric stability and thus boundary-layer decoupling limit the amount of (sensible and latent) heat that can be transmitted from the atmosphere to the snow surface. The strong stability is typically caused by two factors, (i) the temperature difference between the (melting) snow surface and the near-surface atmosphere and (ii) cold-air pooling in topographic depressions. These factors are almost always a prerequisite for perennial snowfields to exist. For the first time, this contribution investigates the relative importance of the two factors in a controlled wind tunnel environment. Vertical profiles of sensible heat and momentum fluxes are measured using two-component hot-wire and one-component cold-wire anemometry directly over the melting snow patch. The comparison between a flat snow surface and one that has a depression shows that atmospheric decoupling is strongly increased in the case of topographic sheltering but only for low to moderate wind speeds. For those conditions, the near-surface suppression of turbulent mixing was observed to be strongest, and the ambient flow was decoupled from the surface, enhancing near-surface atmospheric stability over the single snow patch.

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For the first time, this contribution investigates atmospheric decoupling above melting snow in a wind tunnel study. High-resolution vertical profiles of sensible heat fluxes are measured directly over the melting snow patch. The study shows that atmospheric decoupling is strongly increased in topographic sheltering but only for low wind velocities. Then turbulent mixing close to the surface is strongly suppressed, facilitating the formation of cold-air pooling in local depressions.
For the first time, this contribution investigates atmospheric decoupling above melting snow in...
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