Automatic monitoring of the effective thermal conductivity of snow in a low-Arctic shrub tundraReport as inadecuate

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1 Takuvik Joint ULaval-CNRS Laboratory 2 Centre for Northern Studies - Université Laval 3 Department of Chemistry - Université Laval 4 LGGE - Laboratoire de glaciologie et géophysique de l-environnement 5 Imperial College London 6 Department of Geography 7 Météo-France Paris

Abstract : The effective thermal conductivity of snow, k eff , is a critical variable which determines the temperature gradient in the snowpack and heat exchanges between the ground and the atmosphere through the snow. Its accurate knowledge is therefore required to simulate snow metamorphism, the ground thermal regime, permafrost stability, nutrient recycling and vegetation growth. Yet, few data are available on the seasonal evolution of snow thermal conductivity in the Arctic. We have deployed heated needle probes on low-Arctic shrub tundra near Umiujaq, Quebec, N56 • 34 ; W76 • 29 and monitored automatically the evolution of k eff for two consecutive winters, 2012–2013 and 2013–2014, at four heights in the snowpack. Shrubs are 20 cm high dwarf birch. Here, we develop an algorithm for the automatic determination of k eff from the heating curves and obtain 404 k eff values. We evaluate possible errors and biases associated with the use of the heated needles. The time evolution of k eff is very different for both winters. This is explained by comparing the meteorological conditions in both winters , which induced different conditions for snow metamor-phism. In particular, important melting events in the second year increased snow hardness, impeding subsequent densifi-cation and increase in thermal conductivity. We conclude that shrubs have very important impacts on snow physical evolution: 1 shrubs absorb light and facilitate snow melt under intense radiation; 2 the dense twig network of dwarf birch prevent snow compaction, and therefore k eff increase; 3 the low density depth hoar that forms within shrubs collapsed in late winter, leaving a void that was not filled by snow.

Author: F Domine - M Barrere - D Sarrazin - Stéphane Morin - L Arnaud -



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