Exploring eddy-covariance and large-aperture scintillometer measurements in an Amazonian rain forest

A large-aperture scintillometer (LAS) is used to estimate the surface sensible heat fluxes in an Amazonian rain forest site, and these fluxes are compared with an eddy-covariance system (EC) to analyze conditions of low-frequency modulation in the surface layer. The results show that the flux estimates from the EC are often lower than from the LAS. The differences between EC and LAS tend to increase with decreasing correlation between vertical wind and temperature (rwT). Using different averaging times on EC calculations, we observe that the largest differences between the LAS and the EC fluxes are found for 10-min averages, less so for 30-min averages, while 1-h averages give the smallest differences. The results are attributed to the spatial averaging effect of the LAS. Generally, the results suggest that rwT can be used as an indicator of the importance of low-frequency motions in the surface layer. Evaluating the energy balance for different ranges of rwT, we found that its closure improves when data with increasingly higher rwT are used. In addition, a methodology has been developed to correct the scintillometer signals for the effect of tower vibrations.