A TKE-Based Framework for Studying Disturbed Atmospheric Surface Layer Flows and Application to Vertical Velocity Variance Over Canopies

We propose an approach to study disturbed surface layer flows based on a simplified form of the turbulent kinetic energy (TKE) budget equation (the reduced TKE budget), which can be represented by a two-dimensional phase space. The phase space provides a way to quantify relative contributions of shear and buoyancy production/destruction of TKE, as well as the local imbalance between local production and dissipation. In this framework, Monin-Obukhov Similarity Theory represents one possible approach to reduce the dimensionality of the phase space. We apply this framework to study the vertical velocity variance in the canonical surface layer and in the canopy roughness sublayer above the Amazon forest. Results reveal interesting insight into the behavior of the vertical velocity variance over forests, linking its magnitude to the imbalance between local production and dissipation of TKE. Plain Language Summary The whirling wind motions in the lowest 100 m of the atmosphere play an important role in transporting energy, gases, and particles away from and toward the land surface. These exchanges comprise an important part of the atmosphere-biosphere interaction. Quantifying and predicting the energy available to promote this mixing is critical to better understand the level of interactions between the atmosphere and the biosphere. However, the predictors of energy content are strongly linked to the surface properties, and theories that work over grass fields do not work over forests or urban areas. Thus far, each surface type has been studied separately and some are better understood than others. In this paper we propose the first step toward a more unified description of the energy available to promote vertical mixing valid across different surface types. We use observational data collected over a grass field and over the Amazon rainforest to illustrate the use of this new framework. Further studies will be required to understand its full capabilities and limitations.