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Hydrology and Earth System Sciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/hess-2017-595
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
25 Oct 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Hydrology and Earth System Sciences (HESS).
Revisiting Kelvin Helmholtz Instabilities and von Kármán Vortices in Canopy Turbulence
Tirtha Banerjee1,2, Frederik De Roo2, and Rodman Linn1 1(Current) Earth and Environmental Sciences Division, Los Alamos National Laboratory, New Mexico 87545, USA
2Karlsruhe Institute of Technology (KIT), Institute of Meteorology and Climate Research, Atmospheric Environmental Research (IMK-IFU), 82467 Garmisch-Partenkirchen, Germany
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 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 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.

Citation: Banerjee, T., De Roo, F., and Linn, R.: Revisiting Kelvin Helmholtz Instabilities and von Kármán Vortices in Canopy Turbulence, Hydrol. Earth Syst. Sci. Discuss., https://doi.org/10.5194/hess-2017-595, in review, 2017.
Tirtha Banerjee et al.
Tirtha Banerjee et al.
Tirtha Banerjee et al.

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Short summary
The conceptual model of turbulent flow through vegetation canopies is a phenomenological one that is developed from experimental observations. However, standard numerical simulations of canopy turbulence usually don't resolve the canopy as solid obstructions. We seek to reconcile such numerical simulations with the observations using large eddy simulations and information theory. We find out that the traditional drag based representation contains signatures of the phenomenological model.
The conceptual model of turbulent flow through vegetation canopies is a phenomenological one...
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