Estimation of the nocturnal boundary layer height over the Central Amazon forest using turbulence measurements

The nocturnal boundary layer height (hN) was investigated using one year of data (2022) collected by sonic anemometers installed at 11 heights, above the canopy top on the towers of the Amazon Tall Tower Observatory (ATTO) in Central Amazon. Unlike previous assessments relying on indirect methodologies, in the present study hN was directly estimated from measurements of turbulent fluxes of momentum and kinematic sensible heat. Our findings highlighted the dynamic effect of forest topography: under northeast winds, associated with lower roughness, hN varied between 81 m during very stable stratification and 172 m in neutral conditions. Conversely, under southeast winds, where roughness is higher, hN ranged between 81 and 223 m. These estimates reveal the significant control exerted by atmospheric stability and topography on the hN variability. Interestingly, under neutral and weakly stable stratifications our finds align with the theoretical parameterization proposed in previous works. However, discrepancies emerged in very stable stratification and when the boundary layer structure is influenced by topography.