Abstract
Abstract. Thermal and surface offsets describe mean annual ground temperature relative to mean annual air temperature, and for permafrost modelling they are often predicted as a function of surface characteristics and topography. As macroclimatic conditions influence the effectiveness of the underlying processes, knowledge of surface- and topography-specific offsets is not easily transferable between regions, limiting the applicability of empirical permafrost distribution models over areas with strong macroclimatic gradients. In this paper we describe surface and thermal offsets derived from distributed measurements at seven field sites in British Columbia. Key findings are (i) a surprisingly small variation of the surface offsets between different surface types; (ii) small thermal offsets at all sites (excluding wetlands and peat); (iii) a clear influence of the micro-topography at wind exposed sites (snow-cover erosion); (iv) a north–south difference of the surface offset of 4 °C in vertical bedrock and of 1.5–3 °C on open (no canopy) gentle slopes; (v) only small macroclimatic differences possibly caused by the inverse influence of snow cover and annual air temperature amplitude. These findings suggest that topoclimatic factors strongly influence the mountain permafrost distribution in British Columbia.
Highlights
To estimate permafrost distribution and characteristics, knowledge of site-specific coupling between the lower atmosphere and the ground is needed
Thermal and surface offsets describe mean annual ground temperature relative to mean annual air temperature, and for permafrost modelling they are often predicted as a function of surface characteristics and topography
These findings suggest that topoclimatic factors strongly influence the mountain permafrost distribution in British Columbia
Summary
To estimate permafrost distribution and characteristics, knowledge of site-specific coupling between the lower atmosphere and the ground is needed. Surface offsets (SO), defined as MAGST minus MAAT (where MAGST is the mean annual ground-surface temperature (GST) and MAAT is the mean annual air temperature), and thermal offsets (TO), defined as the mean annual temperature (MAT) at the top of permafrost minus MAGST, are terms to describe this coupling (Smith and Riseborough, 2002). These offsets depend on local climatic and topographic conditions as well as the surface characteristics because these conditions cause a large variability in (solar and long-wave) radiation, snowcover insulation and other phenomena affecting near-surface heat transfer. This study presents the first distributed ground temperature records in potential permafrost areas of this region, which are necessary for such a task
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