DEGREE OF INFLUENCE OF THE BIOT NUMBER OVER NEAR-SURFACE TEMPERATURE ANOMALIES

It is well known to researchers working in geothermal systems that heat loss from shallow hydrothermal fluids can perturb near-surface temperatures. A number of researchers have made use of these temperature changes for qualitative or semi-quantitative analyses (e.g., identification of subsurface flow paths, snowfall calorimetry), but little effort has been expended to develop a quantitative theory of shallow temperature distributions. Here we present a quantitative model linking near-surface temperatures to the temperature and volumetric discharge of shallow hydrothermal fluids. Although previous researchers have pointed out that factors such as insolation and surface albedo can influence the shallow temperature distribution, our model suggests the magnitude of the Biot number (the dimensionless ratio of convective heat loss to the atmosphere and conductive heat transfer in the subsurface) places primary control on the manifestation of near-surface temperature anomalies. Our results indicate that significant near-surface temperature anomalies result from decoupling of ground and atmospheric temperatures at Biot numbers < 10; for greater values of the Biot number, the temperature of the land surface boundary approaches atmospheric, and temperature anomalies are suppressed.