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Warming of permafrost temperatures on Svalbard - what is the effect of the snow cover?

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Citation:
Boike, J. , Westermann, S. , Piel, K. and Overduin, P. P. (2010): Warming of permafrost temperatures on Svalbard - what is the effect of the snow cover? , European Conference on Permafrost, June 13-17, Longyearbyen, Svalbard. .
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Abstract:

1 MOTIVATIONThis contribution investigates the warming of per-mafrost and potential causes: (i) snow cover and physical properties, (ii) soil thermal state before on-set of snowfall (iii) climate parameters such as win-ter air temperatures and radiation balance. The main factors determining the permafrosts heat transfer are: (i) phase composition of soil (specifically avail-able pore space) which enables vapor diffusion and/or water advection during all periods (ii) the temperature gradient between atmosphere and soil which is largely affected by the snow cover. The heat transfer into the ground is largely transmitted via conduction with the exception of snow melt and freeze back. The insulating capacity of snow damp-ens the effect of cold winter air temperatures on the soil. Winter warming events, rain-on-snow events, early-onset snow packs and warm end-of-summer soil conditions can contribute to warmer soil condi-tions throughout the winter. Warmer soils contain more liquid water and respond more slowly to in-creased heat loss to the atmosphere.2 INVESTIGATION AREA AND METHODSWe use hourly data from automated weather and soil and snow temperature/volumetric water content sta-tions from the Bayelva site near Ny-Ålesund. Auxil-iary data include radiation balance data from the BSRN station network in Ny- Ålesund. 3 RESULTSThe 11-year permafrost temperature record from the Bayelva site shows a warming and thawing trend, especially pronounced over the last 5 years. In total, about 50 cm of upper permafrost has been lost at this site over the 11 year period since 1998. It is not clear yet what causes the observed warming trend. Factors considered include changes of the surface energy balance (radiation budget, atmospheric fluxes), changes of the surface characteristics (snow, vegeta-tion cover, wetness), and changes in subsurface composition (ice content, soil material). Further-more, (warm) ocean currents and ice cover dynamics give Svalbard its relatively mild maritime climate. The hourly air temperature data from Ny-Ålesund southeast of the Bayelva site shows a long term pro-nounced winter warming trend (superimposed on strong interannual variability). From 1990 to 2009, the winter (Oct-Apr) temperatures increased by 0.13°C/year, whereas the summer temperatures (Jul-Aug) only increased by 0.05°C/year

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