Investigating the mechanisms responsible for the lack of surface energy balance closure in a central Amazonian tropical rainforest

This work investigates the diurnal and seasonal behavior of the energy balance residual ( E ) that results from the observed difference between available energy and the turbulent fluxes of sensible heat ( H ) and latent heat ( LE ) at the FLUXNET BR-Ma2 site located in the Brazilian central Amazon rainforest. The behavior of E is analyzed by extending the eddy covariance averaging length from 30 min to 4 h and by applying an Information Flow Dynamical Process Network to diagnose processes and conditions affecting E across different seasons. Results show that the seasonal turbulent flux dynamics and the Bowen ratio are primarily driven by net radiation ( R n ), with substantial sub-seasonal variability. The Bowen ratio increased from 0.25 in April to 0.4 at the end of September. Extension of the averaging length from 0.5 (94.6% closure) to 4 h and thus inclusion of longer timescale eddies and mesoscale processes closes the energy balance and lead to an increase in the Bowen ratio, thus highlighting the importance of additional H to E. Information flow analysis reveals that the components of the energy balance explain between 25 and 40% of the total Shannon entropy with higher values during the wet season than the dry season. Dry season information flow from the buoyancy flux to E are 30–50% larger than that from H , indicating the potential importance of buoyancy fluxes to closing E . While the low closure highlights additional sources not captured in the flux data and random measurement errors contributing to E , the findings of the information flow and averaging length analysis are consistent with the impact of mesoscale circulations, which tend to transport more H than LE , on the lack of closure.