Testing energy balance closure with GOES-retrieved net radiation and in situ measured eddy correlation fluxes in BOREAS

GOES satellite-retrieved surface net radiation (R-n) and in situ estimates of surface sensible-latent heat fluxes from eddy correlation measurements are used to test for energy balance closure at the top of the boreal forest. The tests are carried out at five tower flux (TF) sites within the Boreal Ecosystem-Atmosphere Study (BOREAS) experimental area for June-September 1996. The main result is that measured eddy correlation fluxes appear biased low. Surface radiation budget algorithms for directional shortwave/longwave fluxes are used with GOES 8 imager measurements to obtain R-n. The R-n retrievals are made for different types of sky Conditions and validated against in situ measurements obtained at the 10 BOREAS mesonet stations. The analysis indicates an overall bias uncertainty in the satellite-retrieved R-n of approximately +/-7.5%, a value large enough that it could affect our interpretation of the energy balance closure analysis. However, in considering the sign of the all-sky bias, our conclusion that the eddy correlation fluxes are biased low may be understated. Results of the closure analysis are in near agreement to results from a set of seven independent energy balance closure studies conducted at individual BOREAS tower flux sites for 1994, based on in situ tower measurements of the surface flux terms. The agreement suggests that combined sensible-latent heat flux estimates from the TF eddy correlation measurements are approximately 15% low. Also discussed is the implication of these results in helping establish uncertainty bars on the boreal forest component of the global carbon budget.