Abstract
Abstract. The effective thermal conductivity of snow, keff, 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 keff 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 keff from the heating curves and obtain 404 keff values. We evaluate possible errors and biases associated with the use of the heated needles. The time evolution of keff is very different for both winters. This is explained by comparing the meteorological conditions in both winters, which induced different conditions for snow metamorphism. In particular, important melting events in the second year increased snow hardness, impeding subsequent densification 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 keff increase; (3) the low density depth hoar that forms within shrubs collapsed in late winter, leaving a void that was not filled by snow.
Highlights
Snow on the ground acts as a thermally insulating layer which limits ground cooling in winter
Dwarf birch twigs absorb light and modify the local energy budget. All these variations resulted in variations in snow property at the meter scale, noticeable in the degree of melting, the amount, density and grain size of depth hoar, the thickness and hardness of wind slabs, etc
We tentatively suggest that the snow structure was a mixture of depth hoar and melt–freeze crust, and the continuous weakening of this mixed structure during months of temperature gradient metamorphism led to its partial collapse
Summary
Snow on the ground acts as a thermally insulating layer which limits ground cooling in winter. This has large scale and far-reaching implications concerning for example the recycling of soil nutrients and their availability for the subsequent growing season (Saccone et al, 2013; Sturm et al, 2005) and the thermal regime of permafrost (Zhang, 2005). The variable is termed “effective” because besides the fact that it is meant to represent the conductive behavior of snow as a porous medium made of ice and air, which already makes it an effective property, it implicitly includes processes such as heat transfer by latent heat exchanges caused by sublimation. Domine et al.: Automatic monitoring of the effective thermal conductivity of snow and condensation during snow metamorphism (Sturm et al, 1997)
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