A TKE analysis for the roughness sublayer of an Amazon forest under unstable atmospheric conditions
DOI:
https://doi.org/10.5902/2179460X87711Keywords:
Turbulence Kinetic Energy, Roughness Sublayer, Atmospheric Turbulence, Forest Canopy, Monin-Obukhov Similarity TheoryAbstract
The equation of turbulence kinetic energy (TKE) quantifies the intensity of turbulence, the mechanisms generating it, transporting it, and dissipating it. Given the well-known difficulty in applying Monin-Obukhov Similarity Theory in the roughness sublayer, the development of new approaches to understand the flow in this region of the atmosphere is necessary. By calculating the terms of TKE and their balance using a reduced TKE diagram, we sought to investigate the characteristics of turbulence over an Amazon forest located at the ATTO Project experimental site. To do so, using data from three sonic anemometers at heights of 35m, 50m and 81m installed on one of the experiment towers and collected between August and October 2021 for the daytime period, we computed the terms of mechanical production P , thermal production B, storage S, vertical turbulence transport Tv, and dissipation εe of TKE. At the chosen analysis height (66m - average between the two upper sonic anemometers) and after quality control, we obtained 42 one-hour blocks. It was observed that in over 90% of the cases, εe was the largest term. The second-largest term was B (≈ 57%) and the third was P (≈ 40%), showing a certain balance regarding production mechanisms. However, upon balancing them, the existence of a residual term, not explained by Tv, was found. This residual was predominantly negative, which may indicate the effect of vegetation and topography on the flow. It was also noted that in 70% of the blocks, the transport of TKE was upwards. S, on the other hand, is at least 2 orders of magnitude smaller than P , being negligible. Additionally, we calculated the dimensionless standard deviation for vertical wind speed, which showed good agreement with what is expected in the inertial sublayer (ISL).
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