Detecting small changes (< 0.1 Wm-2) in the surface energy flux from borehole temperatures

Borehole temperature data has successfully been used to resolve past climatic change but traditionally the result has been stated as a function of ground surface temperature (GST), leaving a gap with its relationship to more standard meteorological climate chance indices. We report progress in a calibration study, begun in 1993, to link GST with surface energy budgets and attempt to resolve the radiative forcing from greenhouse gases. Two approaches are being followed: (1) an observational study of temperature coupling between the ground surface and the standard meteorological variables and, (2) construction of a energy balance model that accounts for time-varying thermal properties, solar radiation, precipitation, snowfall and soil type. The observational data consist of 30-min meteorologic and subsurface temperature measurements at two contrasting sites, a dry steppe environment in western Utah, and a moist, temperate location in the outskirts of Prague, Czech Republic. Both stations have been operating for three years, and the temperature coupling between air and ground is largely determined by solar radiation in summer months and soil moisture in winter months. Intense instantaneous energy fluxes at the surface ({approximately} 1000 W m-2), along with distinct thermal properties between the air and ground, generate the high variability inmore » temperature tracking on short time scales. However, the longer century-scale linkage between GST and climate chance is obtained from careful in-situ investigation of the material thermal properties and and measurement of the thermal perturbation in the subsurface. Our results suggest that a single borehole temperature data can resolve transient surface heat flux chances that are less than 0.1 Wm-2 per century.« less