Journal cover Journal topic
The Cryosphere An interactive open-access journal of the European Geosciences Union
The Cryosphere, 5, 945-959, 2011
© Author(s) 2011. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
26 Oct 2011
Modeling the impact of wintertime rain events on the thermal regime of permafrost
S. Westermann1, J. Boike2, M. Langer2, T. V. Schuler1, and B. Etzelmüller1 1Department of Geosciences, University of Oslo, P.O. Box 1047, Blindern, 0316 Oslo, Norway
2Alfred-Wegener-Institute for Polar and Marine Research, Telegrafenberg A43, 14473 Potsdam, Germany
Abstract. In this study, we present field measurements and numerical process modeling from western Svalbard showing that the ground surface temperature below the snow is impacted by strong wintertime rain events. During such events, rain water percolates to the bottom of the snow pack, where it freezes and releases latent heat. In the winter season 2005/2006, on the order of 20 to 50% of the wintertime precipitation fell as rain, thus confining the surface temperature to close to 0 °C for several weeks. The measured average ground surface temperature during the snow-covered period is −0.6 °C, despite of a snow surface temperature of on average −8.5 °C. For the considered period, the temperature threshold below which permafrost is sustainable on long timescales is exceeded. We present a simplified model of rain water infiltration in the snow coupled to a transient permafrost model. While small amounts of rain have only minor impact on the ground surface temperature, strong rain events have a long-lasting impact. We show that consecutively applying the conditions encountered in the winter season 2005/2006 results in the formation of an unfrozen zone in the soil after three to five years, depending on the prescribed soil properties. If water infiltration in the snow is disabled in the model, more time is required for the permafrost to reach a similar state of degradation.

Citation: Westermann, S., Boike, J., Langer, M., Schuler, T. V., and Etzelmüller, B.: Modeling the impact of wintertime rain events on the thermal regime of permafrost, The Cryosphere, 5, 945-959, doi:10.5194/tc-5-945-2011, 2011.
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