Towards Inclusion of Sub-grid Variability of Snow in Distributed Permafrost Models

Wednesday, 17 December 2014: 5:15 PM
Kjersti Gisnas, Sebastian Westermann, Thomas Schuler and Bernd Etzelmuller, University of Oslo, Department of geosciences, Oslo, Norway
High altitude environments are often exposed to strong winds, thus drifting snow can create a small-scale pattern of highly variable snow heights. This has profound implications for the ground thermal regime. Variability in mean annual ground surface temperatures of up to 6°C within areas of 1 km2 have been documented from Svalbard and Norway earlier, and can to a large degree be explained by variation of maximum snow heights. Land surface models or permafrost models employing an average snow height per grid cell of e.g. 1 km2or larger are not capable of representing such local-scale variability.

This study presents a robust scheme where we statistically represent the sub-grid variability of ground surface temperatures and demonstrate that we can reproduce the distribution within a grid cell. This is achieved by (1) applying a simple terrain parameter (Winstral et al., 2002) on a 10 meter DEM, estimating exposure from a selected wind direction. The degree of exposure is estimated for main wind directions over the winter season, derived from HINDCAST 10 m wind direction data (ERA40 reanalysis downscaled using HIRLAM, Norwegian Meteorological Institute), available at approximately 11 km (0.1 degree) spatial resolution and 2 hour temporal resolution back to 1957. Here we obtain a statistical representation of the distribution of maximum snow heights. (2) we use this information for calculating ground temperature distributions within the grid cells using a simple equilibrium permafrost model (CryoGRID 1). Finally, we test this approach at four 100 km2sized areas where we have extensive field observations, located along a latitudinal transect in Norway. We demonstrate that the inclusion of a snow distribution function within each grid-cell clearly improves the representation of permafrost coverage in high latitude areas.

Winstral, A., K. Elder, and R. E. Davis. 2002. Spatial snow modeling of wind-redistributed snow using terrain-based parameters, Journal of Hydrometeorology, 3: 524-538.