An examination of short- and long-term air-ground temperature coupling

Data from two experimental air-ground climate stations operating at field and wooded sites in Nova Scotia (Canada), monitoring meteorological and ground thermal variables, were examined along with longer-term records of air and soil temperature in order to clarify the energy exchanges at the air-ground interface. A simple, first-order approximation, multilayer numerical model of heat conduction was used to assess whether soil temperatures track air temperature variations at each location. Data indicate that in winter, when soil freezing occurs, the heat transfer regime between the lower atmosphere and the ground is dominated by latent heat released at field and wooded sites. In spring and summer, the ground thermal response at the field site is driven by direct solar radiation heating rather than by conduction. Results from a numerical model indicate that during a frost-free period of 290 days in spring, summer and fall, the soil thermal regime in the forest can be modelled using surface air temperature data as the driver at the upper boundary and assuming a purely conduction dominated scenario, such that at these short time scales, the forest floor and lower atmosphere appear to be coupled. Longer-term records (similar to 30 years) from selected climatological stations across Canada indicate that soil-air temperature differences appear to be temporally variable at all locations examined. If this variation is common and persistent, then the coupling between air and ground temperatures may not be as straight forward as previously though at some locations. (C) 2003 Elsevier B.V. All rights reserved.