Nocturnal Thermodynamics and Dynamics of the Amazon Boundary Layer Using Single Column Model Simulations

The Amazon rainforest plays a crucial role in both regional and global climates, due to its size and its influence on trace gas dynamics. Understanding the forest's influence on local gas concentrations and vertical transport is vital for estimating the chemical processes in ecosystem models. The Amazon boundary layer, influenced by turbulent processes, links the forest to the upper atmosphere, affecting the diffusion and vertical transport of momentum, energy, and scalars such as trace gases and water vapor. However, during the night, turbulence decreases due to stable stratification, leading to a significant reduction in turbulent fluxes and vertical transport. This study aims to use a single-column model to describe the thermodynamics and dynamics of the Amazon nocturnal boundary layer, taking into account the role of radiative processes. The model includes prognostic equations for the two wind components, potential temperature, and a passive scalar. Turbulent fluxes are parameterized using K-theory, with a 1.5-order closure that incorporates a prognostic equation for turbulent kinetic energy. The prognostic equations are discretized on a vertical grid, with the influence of the forest included by adding mechanical and thermal terms to the wind component and temperature prognostic equations up to the tree height level. Boundary conditions and initial profiles were derived from observational data obtained at the Amazon Tall Tower Observatory (ATTO) in Amazonas State, Brazil. Simulations of contrasting nights, using two distinct turbulence length scales in the model, were conducted to evaluate the model's performance under varying turbulence conditions. The results indicate that when using a turbulence length scale that suppresses turbulence under strong stable conditions, the model simulates a shallow boundary layer with reduced turbulent fluxes. The issues of boundary layer height and the nocturnal jet are also addressed.