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How much snow is lost to sublimation?

Contact: Christine Groot-Zwaaftink (groot@slf.ch)

Contents 1 How much snow is lost to sublimation? 1.1 Overview 1.2 Publications

This experiment is associated with the following fieldsites/deployments/measurement locations:
Fieldsites/deployments:
Wannengrat (link: Home)
Measurement locations:
Tib1 (http://www.swiss-experiment.ch/index.php/Wannengrat:Tib1) Tib2 (http://www.swiss-experiment.ch/index.php/Wannengrat:Tib2) Tib3 (http://www.swiss-experiment.ch/index.php/Wannengrat:Tib3)	Photos Videos Wikipedia Webcams

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Overview

An unanswered question in the mass balance of polar regions and the alpine snowpack is: how much snow is returned to the atmosphere in the form of water vapour? The water content of the atmosphere as well as the formation and conservation of powerful ice sheets and glaciers all depend on this evaporation, which is particularly intensive during periods of snow drift.

SLF carries out investigations into this process through field measurements, numerical modelling and wind tunnel experiments. A collaboration of Swiss (SLF) and Japanese scientists provided a first breakthrough in the understanding of the evaporation processes, by quantitatively reproducing them in a wind tunnel experiment. This experiment showed that the influence of snow drift is far larger than described by previous models.

Particularly large quantities of vapour are produced when strongly dentritic (ramified) snow crystals are present as well as during strong solar radiation periods. Initial model calculations showed that during periods with medium wind speeds (5ms-1) and/or medium relative humidity (70%), approx. 1 cm of snow can evaporate per day. Scientists are now trying to improve understanding of the mechanisms involved in the evaporation and hence provide better forecasts on the role of evaporation, particularly in mountainous areas. Wind tunnel experiments of drifting snow sublimation

Experiments in a cold wind tunnel are used to verify drifting snow sublimation models. A layer of drifting snow particles is formed over a sintered snow surface. Sublimation and drifting snow flux is estimated from two, vertically resolved profile measurements separated along the flow path, and compared to a simple, one-dimensional diffusion model of the drift and drifting snow sublimation. The experiments show an increase in water vapor content of the air from drifting snow sublimation. The measured drifting snow sublimation effect appeared to be larger than theoretical values found in the model study. Under wind tunnel conditions, particle number density appears to be the controlling factor on the sublimation rate. For experiments with external solar radiative forcing, the increase of the sublimation rate is larger than theoretical predictions. The experiments suggest that irregular snow crystals and solar radiation might increase the sublimation rate more than described by many drifting snow models. For more information see Wever et al. (2009).

Wever, N., Lehning, M., Clifton, A., Rüedi, J.-D., Nishimura, K., Yamaguchi, S., Nemoto, M., Sato, A., 2009. Verification of moisture budgets during drifting snow conditions in a cold wind tunnel, Water Resources Res., 45, doi:10.1029/2008WR007522. Lagrange model development to describe drifting snow and drifting snow sublimation

A Lagrangian dispersion model is developed to correctly describe the transition from saltation to suspension (modified saltation) and to allow the reconstruction of small scale erosion and deposition patterns. The approach is based on a modified Langevin equation, which can take into account partly resolved turbulence from a LES model. A new feature of the model will be that heat- and mass transfer equations will be coupled to the transport equation to allow the calculation of sublimation during snow transport. This approach will improve current estimations of sublimation of drifting and blowing snow, which heavily depends on the particle number density. Using standard models of meteorology (ARPS) and advanced LES codes, the influence of mean flow and resolved turbulent eddies on the snow distribution will be studied.

Publications

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• Drifting snow sublimation - A high-resolution 3-D model with temperature and moisture feedbacks (C.D. Groot-Zwaftink, H. Löwe, R. Mott, M. Bavay, M. Lehning, Drifting snow sublimation - A high-resolution 3-D model with temperature and moisture feedbacks, JGR Atmospheres, 116, D16107, doi: 10.1029/2011JD015754., 1 October 2011)
• The Effect of Drifting Snow Sublimation in Mountains (C.D. Groot-Zwaaftink, R. Mott, H. Lowe, N. Dawes, M. Lehning, The Effect of Drifting Snow Sublimation in Mountains, IUGG, 7 July 2011)