Observations of radiation exchange above and below Amazonian forest

Measurements of shortwave and longwave components of the radiation budget were made above and below tropical forest in the Amazon Basin for a total duration of 203 hours in September 1983. Albedo was (12.25±0.2)%, and showed a small variation with solar altitude. The net outward flux of longwave radiation was around 30 W m⁻², and fairly constant over the day. The relationship between net radiation, R, and solar radiation, S, was adequately described by the expression R = (0.858±0.006)S ‐ (35.0±1.9) (W m⁻²). The fraction of solar radiation reaching the bottom of the canopy was low, about one per cent: net radiation in this position was consistent with low soil heat flux and low soil evaporation.