Coherent structures detection within a dense alpine forest
Date
2022-09-29Primeiro coorientador
Mortarini, Luca
Primeiro membro da banca
Dias Júnior, Cleo Quaresma
Segundo membro da banca
Acevedo, Otavio Costa
Terceiro membro da banca
Maroneze, Rafael
Quarto membro da banca
Costa, Felipe Denardin
Metadata
Show full item recordAbstract
The influence of coherent vortices on the turbulence structure and momentum flux is investigated
inside a coniferous forest on an Alpine Plateau. The presence of coherence structure and their
characteristic timescales are detected by fitting the vertical velocity auto-correlation functions
with a theoretical oscillating function. This allowed to discriminate between turbulent data
subsets characterized by fine-scale turbulence and data subsets in which turbulence is dominated
by coherent vortices generated at the canopy top. Five different stability regimes, from free
convection to very stable stratification, were considered in the analysis. An original methodology
for fitting cross-correlation function in presence of periodic behaviours is developed and applied
to the turbulent momentum flux. The analysis shows how not far from neutral conditions the
most energetic time scale of the momentum flux is mainly determined by the longitudinal wind
velocity component, rather than vertical one, while in free convection and very stable conditions
coherent vortices do not seem to influence the momentum transport, dominated by large scale
structures. This is confirmed by the fine-scale turbulence and coherent structures efficiency in
turbulence transport throughout the stability regimes. Finally, the oscillation of the auto and
cross-correlation functions of the wind velocity components in presence of coherent structures is
justified by means of a simplified Lagrangian stochastic model.
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