Linking Meteorology, Turbulence, and Air Chemistry in the Amazon Rain Forest

Quart J Royal Meteoro Soc

Katul

2019

Self Cite

The significance of air flow within dense canopies situated on hilly terrain is not in dispute given its relevance to a plethora of applications in meteorology, wind energy, air pollution, atmospheric chemistry and ecology. While the mathematical description of such flows is complex, progress has proceeded through an interplay between experiments, mathematical modelling, and more recently large‐eddy simulations (LESs). In this contribution, LES is used to investigate the topography‐induced changes in the flow field and how these changes propagate to scalar transport within the canopy. The LES runs are conducted for a neutral atmospheric boundary layer above a tall dense forested canopy situated on a train of two‐dimensional sinusoidal hills. The foliage distribution is specified using leaf area density measurements collected in an Amazon rain forest. A series of LES runs with increasing hill amplitude are conducted to disturb the flow from its flat‐terrain state. The LES runs successfully reproduce the recirculation region and the flow separation on the lee‐side of the hill within the canopy region in agreement with prior laboratory and LES studies. Simulation results show that air parcels released inside the canopy have two preferential pathways to escape the canopy region: a “local” pathway similar to that encountered in flat terrain and an “advective” pathway near the flow‐separation region. Further analysis shows that the preferential escape location over the flow‐separation region leads to a “chimney”‐like effect that becomes amplified for air parcel releases near the forest floor. The work here demonstrates that shear‐layer turbulence is the main mechanism exporting air parcels out the canopy for both pathways. However, compared to flat terrain, the mean updraught at the flow separation induced by topography significantly shortens the in‐canopy residence time for air parcels released in the lower canopy, thus enhancing the export fraction of reactive gases.

Section: Methodsmentioning

confidence: 96%

Section: Methodsmentioning

confidence: 99%

Effects of topography on in‐canopy transport of gases emitted within dense forests

Chen

Quart J Royal Meteoro Soc

Katul

2019

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“…For this purpose, we employed the AHATS (Salesky & Chamecki, 2012; University Corporation for Atmospheric Research-National Center for Atmospheric Research-Earth Observing Laboratory, 1990) and the GoAmazon (Freire et al, 2017;Fuentes et al, 2016) data sets. For this purpose, we employed the AHATS (Salesky & Chamecki, 2012; University Corporation for Atmospheric Research-National Center for Atmospheric Research-Earth Observing Laboratory, 1990) and the GoAmazon (Freire et al, 2017;Fuentes et al, 2016) data sets.…”

Section: Application To Field Datamentioning

confidence: 99%

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

Geophysical Research Letters

Dias

Freire

2018

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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.

“…Data from the GoAmazon experiment (Fuentes et al . ) are used to test the existence of turbulence and its characteristics in the transport‐enabled region predicted by Equation . This dataset consists of wind velocity (three components) and virtual temperature measured at 20 Hz by nine sonic anemometers (model CSAT3, Campbell Scientific, Inc., Logan, UT) mounted on a 50 m tower in the Amazon rainforest.…”

Section: Field Datamentioning

confidence: 99%

Critical flux Richardson number for Kolmogorov turbulence enabled by TKE transport

Freire

Quart J Royal Meteoro Soc

Bou‐Zeid

et al. 2019

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In stably stratified flows, the flux Richardson number Ri f is a measure of the ratio between buoyancy destruction and shear production of turbulent kinetic energy (TKE). In flows with local equilibrium between shear production, buoyancy destruction and dissipation of TKE, the critical Ri f,c ≈0.21 corresponds to the limit above which Kolmogorov turbulence can no longer be sustained. Analysis of the TKE and velocity variance budget equations shows that the critical Ri f,c is increased by the presence of positive turbulent transport of TKE. This situation is observed, for example, in the roughness sublayer above plant canopies, as demonstrated using field data from the Amazon rainforest.