Modelling the effect of surface hoar formation on the temperature gradient and vapor pressure gradient in a snowpack
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Buried surface hoar layers and faceted crystals are both typical persistent weak layers for initiating an avalanche. Faceted crystals are formed under large vapor pressure gradients which are made by large temperature gradients. This paper discusses what effect the latent heat release from surface hoar growth has on the temperature gradients and corresponding vapor pressure gradients in the snowpack. This was investigated using an automatic weather station placed at Hollekvebrui in Sogndalsdalen, Norway, and measuring the surface hoar formed during a night through mass change of the top 10 cm of snow at the same location. The data gathered was used to develop a numerical simulation that solves the heat equation in one dimension using the finite difference method. The model was developed in several steps that each were modified to calibrate it to more realistic levels. In the final model data inputs from the weather station and mass difference were implemented, and the model shows that a mass gain of 0.094 kg has little effect on the temperature and vapor pressure gradients in the snowpack. However, problems have been found with some of the assumptions that were made around heat transfer in and out of the snowpack, and extending the currently inadequate dataset is necessary to test the findings in this paper.