Investigating the structure of the Atmospheric Boundary Layer over the Amazon Forest in stable and unstable stratication through a Cospectral Budget Model

Given its vital importance in the global climate system, the Amazon region has attracted signicant scientic attention and has been extensively studied in recent years. Both inside and above the forest, nearly all physical, chemical, and biological processes are inuenced by the atmospheric ow structure. Understanding this structure is complicated by the interplay of the tall and dense canopy with the local topography, which may introduce height-dependent mean pressure gradients.In particular, the classical structure—in which a roughness sublayer is overlain by an inertial layer and an outer layer—has been questioned in conditions far from neutral stratication. Measurements at the Amazon Tall Tower Observatory (ATTO) in Brazil showed that, due to the impingement of convective structures from the outer layer in unstable stratication and due to the penetration of low-frequency submeso structures in stable stratication, the presence of an inertial sublayer is dicult to infer. In this work, the vertical structure of the Atmospheric ow is linked to the shape of the vertical velocity spectrum by means of a scale-wise co-spectral budget model that balances mechanical production to pressure-decorrelation and longitudinal buoyancy production (or destruction) in the co-spectral budget for momentum. The model offers a new, original perspective in which the energetic of the momentum ux at low wave-numbers depends on buoyancy through the horizontal heat ux cospectrum, identifying the wave-number at which this contribution cannot be neglected. Plain-Language Summary: The Amazon rainforest is a hot spot for climate change and all the processes happening in th forest are heavily inuenced by how the wind ows through and above it. The wind can be thought of as the means by which the forest communicates with the atmosphere. This is why this works aims at understanding the structure of the wind ow above a dense and tall forested https://agu.confex.com/agu/agu24/a/papers/index.cgi?username=1591920&password=*cookie 1/3 31/07/2024, 16:16 Submission Proof canopy, like the Amazon, introducing a new perspective. Measuring in the Amazon is challenging, but this study was made possible thanks to the Amazon Tall Tower Observatory (ATTO). The ATTO site is located in a pristine area within the Brazilian Amazon, where two meteorological towers, the taller one reaching 325 meters, have been continuously collecting data since 2021.