Soil heat flux and temperature profiles under Amazonian rain forest during the wet season of 1999

Soil temperature influences most of the processes of the soil-plant continuum, and the soil heat flux is a minor, but not negligible component of the surface energy balance under the forest canopy. Thus, soil heat flux profiles were measured at the Rebio-Jaru Amazon Rain Forest site (10°04' S; 61°56' W) during the wet season campaign of 1999 (January-March), as part of the LBA-Large Scale Biosphere -Atmosphere Experiment in Amazonia. In no rain days the temperature shows a regular daily cycle, with an amplitude of about 2°C at the depth of 2cm, while it becomes practically constant at the depth of 40cm; on the other hand, the occurrence of rain causes an immediate change in the soil temperature, "flattening" it. The heat flux also shows a daily cycle, with maxima of the order of 40 Wm-2 in no rain days, and there is a strong change after the onset of rain. Finally, apparent soil thermal diffusivities are also computed and correlated with soil moisture data measured at the site.