Soil heat flux plates are a standard method of measuring soil heat flux in energy balance and related studies. Recent work has suggested that heat flux plates significantly underestimate the true flux value in permafrost terrain. Using data from two sites near Churchill, Manitoba, collected over two summer thaw periods, the Calorimetric method of soil heat flux determination is used to assess the reliability of heat flux plate data. It is found that the heat flux plates underestimate the surface heat flux in organic permafrost terrain by about 50 per cent. The most likely cause of the error appears to be a combination of poor thermal contact between the plate and the peat soil, and possible vapour transport through the porous material. Recommendations are made to reduce errors in field determinations of soil heat flux.
The calorimetric calculations indicate that the largest portion of the soil heat flux is stored as latent heat in the thawing of ground ice. The flux at 1.5m depth constitutes a significant portion of the surface flux. The smallest component of the surface flux is the portion stored as sensible heat in the layer between the surface and the 1.5 m depth. Overall, the soil heat flux represents a high fraction (from 16 per cent to 18 per cent) of the net all-wave radiation available at the surface. KEY WORDS Soil heat flux Permafrost Heat flux plates Organic terrain Energy balance. NOMENCLATURE Parameters for unfrozen water content vs temperature relationship. volumetric heat capacity (MJ m -"C-'). volumetric heat capacity of soil solids (MJ m-3 "(I-').
soil enthalpy (MJ m-3). soil heat flux density (W m-'). time (s). temperature ("C). volume fraction of soil solids. depth (m). thermal conductivity (thawed, frozen) (W m-' T -'). water content (volume fraction). unfrozen water content at sub-zero temperature. apparent volumetric heat capacity (MJ m -3 'C-1.