Turbulence structure in a deciduous forest

Baldocchi, Dennis; Meyers, Tilden P.

doi:10.1007/bf00121712

Cited by 220 publications

(149 citation statements)

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“…2). Ideally, the number of events detected would be constant for a range of threshold parameters as in (Wells, 1998); however, this is not true for turbulence above forest canopies (Baldocchi and Meyers, 1988). As in Baldocchi and Meyers (1988), we found that the number of events and event duration decreases as H increases (Fig.…”

Section: Appendix a Quadrant Hole (Q-h) Methods And Sensitivity Studymentioning

confidence: 65%

“…Rather than tune H to agree with the wavelet analysis, we used a constant H (H = 1) for our analysis as determined by other studies to be a suitable threshold value (Bogard and Tiederman, 1986;Comte-Bellow et al, 1978). Sensitivity of our results to H was evaluated; similar to other studies, we found the number of events decreases quickly with larger hole sizes (see Appendix A) (Baldocchi and Meyers, 1988;Bergstrom and Hogstrom, 1989;Mortiz, 1989;Shaw et al, 1983;Zhu et al, 2007). Multiple detections occurring from the same event are separated from independent events using a time frequency parameter (τ ).…”

Section: Quadrant-hole (Q-h) Analysismentioning

confidence: 90%

“…It has been applied to study canopy turbulence in crop (Finnigan, 1979;Shaw et al, 1983;Zhu et al, 2007) and forest ecosystems (Baldocchi and Meyers, 1988;Bergstrom and Hogstrom, 1989;Gardiner, 1994;Mortiz, 1989;Thomas and Foken, 2007). Q-H analysis provides information about turbulent structures by separating the fluctuating velocity components (u and w ) into four categories based on sign.…”

Section: Quadrant-hole (Q-h) Analysismentioning

confidence: 99%

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Analysis of coherent structures and atmosphere-canopy coupling strength during the CABINEX field campaign

et al. 2011

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Abstract. Intermittent coherent structures can be responsible for a large fraction of the exchange between a forest canopy and the atmosphere. Quantifying their contribution to momentum and heat fluxes is necessary to interpret measurements of trace gases and aerosols within and above forest canopies. The primary objective of the Community Atmosphere-Biosphere Interactions Experiment (CABINEX) field campaign (10 July 2009 to 9 August 2009) was to study the chemistry of volatile organic compounds (VOC) within and above a forest canopy. In this manuscript we provide an analysis of coherent structures and canopy-atmosphere exchange during CABINEX to support in-canopy gradient measurements of VOC. We quantify the number and duration of coherent structure events and their percent contribution to momentum and heat fluxes with two methods: (1) quadrant-hole analysis, and (2) wavelet analysis. Despite differences in the duration and number of events, both methods predict that coherent structures contribute 40-50 % to momentum fluxes and 44-65 % to heat fluxes during the CABINEX campaign. Contributions associated with coherent structures are slightly greater under stable atmospheric conditions. By comparing heat fluxes within and above the canopy, we determine the degree of coupling between upper canopy and atmosphere, and find that they are coupled the majority of the time. Uncoupled canopyatmosphere events occur in the early morning (4-8 a.m. local time) approximately 30 % of the time. This study conCorrespondence to: A. L. Steiner (alsteiner@umich.edu) firms that coherent structures contribute significantly to the exchange of heat and momentum between the canopy and atmosphere at the CABINEX site, and indicates the need to include these transport processes when studying the mixing and chemical reactions of trace gases and aerosols between a forest canopy and the atmosphere.

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Section: Appendix a Quadrant Hole (Q-h) Methods And Sensitivity Studymentioning

confidence: 65%

Section: Quadrant-hole (Q-h) Analysismentioning

confidence: 90%

Section: Quadrant-hole (Q-h) Analysismentioning

confidence: 99%

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Analysis of coherent structures and atmosphere-canopy coupling strength during the CABINEX field campaign

et al. 2011

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“…1b). In some forest canopies, the vertical gradients of U may be sharp except for within the vicinity of its local maximum (e.g., according to the nocturnal mean wind-speed profile in Baldocchi and Meyers 1998). In this situation, the fitting approach (10) should be applied to the region below the local maximum of C d mod and with small vertical gradients of U .…”

Section: A Practical Approach To Estimating the Streamwise Mean Pressmentioning

confidence: 99%

Estimating the Instantaneous Drag–Wind Relationship for a Horizontally Homogeneous Canopy

Pan

Chamecki

Nepf

2016

Boundary-Layer Meteorol

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The mean drag-wind relationship is usually investigated assuming that field data are representative of spatially-averaged metrics of statistically stationary flow within and above a horizontally homogeneous canopy. Even if these conditions are satisfied, large-eddy simulation (LES) data suggest two major issues in the analysis of observational data. Firstly, the streamwise mean pressure gradient is usually neglected in the analysis of data from terrestrial canopies, which compromises the estimates of mean canopy drag and provides misleading information for the dependence of local mean drag coefficients on local velocity scales. Secondly, no standard approach has been proposed to investigate the instantaneous drag-wind relationship, a critical component of canopy representation in LES. Here, a practical approach is proposed to fit the streamwise mean pressure gradient using observed profiles of the mean vertical momentum flux within the canopy. Inclusion of the fitted mean pressure gradient enables reliable estimates of the mean drag-wind relationship. LES data show that a local mean drag coefficient that characterizes the relationship between mean canopy drag and the velocity scale associated with total kinetic energy can be used to identify the dependence of the local instantaneous drag coefficient on instantaneous velocity. Iterative approaches are proposed to fit specific models of velocity-dependent instantaneous drag coefficients that represent the effects of viscous drag and the reconfiguration of flexible canopy elements. LES data are used to verify the assumptions and algorithms employed by these new approaches. The relationship between mean canopy drag and mean velocity, which is needed in models based on the Reynolds-averaged Navier-Stokes equations, is parametrized to account for both the dependence on velocity and the contribution from velocity variances. Finally, velocity-dependent drag coefficients lead to significant variations of the calculated displacement height and roughness length with wind speed. B Marcelo Chamecki

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“…Several other works have contributed to the understanding of this canonical structure of homogeneous canopy flows (Wilson and Shaw, 1977;Finnigan, 1979;Antonia, 1981;Raupach, 1981a;Denmead and Bradley, 1985;Baldocchi and Meyers, 1988;Wilson, 1988;Gao et al, 1989;Holland, 1989;Shaw et al, 1989;Wilson, 1989;Shaw and Schumann, 1992;Kaimal and 20 …”

mentioning

confidence: 99%

Revisiting Kelvin Helmholtz Instabilities and von Kármán Vortices in Canopy Turbulence

Banerjee

Roo

Linn

2017

Preprint

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Abstract. Studying turbulence in vegetation canopies is important in the context of a number of micrometeorological and hydrological applications. While recent focus has shifted more towards exploring different kinds of canopy heterogeneities, there are still gaps in the existing knowledge on the multiple types of dynamics involved in the case of horizontally homogeneous canopies. For example, experimental studies have indicated that turbulence in the canopy sublayer (CSL) can be divided into three regimes. In the deep-zone, the flow-field is dominated by von Kármán vortex streets and interrupted by strong sweep 5 events. The second zone near the canopy top is dominated by attached eddies and Kelvin-Helmholtz waves associated with the velocity inflection point in the mean longitudinal velocity profile. Above the canopy, the flow resembles classical boundary layer flow. In this study, these different kinds of dynamics are studied together by means of a large eddy simulation (LES).The main theme of this work is to address the question whether the parametrization of the canopy by a distributed drag force in numerical simulations instead of placing real solid obstacles is consistent with the three layer conceptual model. Unique 10 techniques such as measures from information theory and coupled oscillator analysis are used to extract the coherent structures associated with the two motions. It can be stated that a better understanding of the rich dynamics associated with the simplest case of canopy turbulence can lead to more efficient simulations and more importantly improve the interpretation of more complex scenarios.

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Turbulence structure in a deciduous forest

Cited by 220 publications

References 37 publications

Analysis of coherent structures and atmosphere-canopy coupling strength during the CABINEX field campaign

Analysis of coherent structures and atmosphere-canopy coupling strength during the CABINEX field campaign

Estimating the Instantaneous Drag–Wind Relationship for a Horizontally Homogeneous Canopy

Revisiting Kelvin Helmholtz Instabilities and von Kármán Vortices in Canopy Turbulence

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