On Lagrangian dispersion of 222Rn, H2O and CO2 within the Amazon rain forest

The present study focuses on the description of the vertical dispersion of trace gases within the Amazon rain forest. A Lagrangian approach is parameterised using in-canopy turbulence measurements made at a site in Rondônia (Reserva Jaru). In contrast to common scaling schemes that solely depend on friction parameters measured above the canopy, a combined scaling that also includes night-time free convective mixing in the lower part of dense vegetation canopies is proposed here. 222Rn concentration profiles and soil flux measurements made at a second site near Manaus (Reserva Cuieiras) are used to evaluate the derived parameterisation and the uncertainties of the forward (prediction of concentration profiles) and inverse (prediction of vertical source/sink distributions) solution of the transfer equations. Averaged day- and night-time predictions of the forward solution agree with the observations within their uncertainty range. During night-time, a weak, but effective free convective mixing process in the lower canopy ensures a relatively high flushing rate with residence times of