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Thermal conductivity of anisotropic snow measured by three independent methods

DOI: 10.5194/tcd-6-1839-2012

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Abstract:

The thermal conductivity of snow determines the temperature gradient, and by this the rate of snow metamorphism. It is therefore a key property of snow. However, parameterizations of thermal conductivity measured with the transient needle probe and the steady-state heat-flux plate show a bias. In addition, it is not clear to which degree thermal anisotropy is relevant. Until now, no physically convincing argument for the existence of this bias could be found. In this study, we investigated three independent methods to measure snow thermal conductivity and its anisotropy: a needle probe with a long heating time, a guarded heat flux plate, and direct numerical simulation at the level of the pore and ice structure. The three methods were applied to identical snow samples, apart from the different measurement volumes of each methods. We analyzed the consistency and the difference between these methods. We found a distinct change from horizontal thermal anisotropy in small rounded grains and vertical anisotropy in depth hoar. The anisotropy between vertical and horizontal conductivity ranges between 0.5–2. This anisotropy can cause a difference of up to 25 % to + 25 % if the thermal conductivity is calculated only from a horizontally inserted needle probe. Based on these measurements, the direct numerical simulation is the most reliable method as the tensorial components of the thermal conductivity can be calculated, the corresponding microstructure is precisely known and the homogeneity of the sample can be determined.

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