Coherent eddies and turbulence in vegetation canopies the mixing layer analogy
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Coherent Eddies and Turbulence in Vegetation Canopies: The mixing-layer analogy. M.R.Raupach, J.J.Finnigan and Y.Brunet Boundary-Layer Meteorology 78: 351-382, 1996. Objectives.

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Coherent eddies and turbulence in vegetation canopies the mixing layer analogy

Coherent Eddies and Turbulence in Vegetation Canopies: The mixing-layer analogy

M.R.Raupach, J.J.Finnigan and Y.Brunet

Boundary-Layer Meteorology 78: 351-382, 1996


Objectives
Objectives mixing-layer analogy

  • This paper argues that the turbulence near the top of the canopy is similar to that of a plane mixing layer rather than of the boundary layer


The mixing layer
The Mixing Layer mixing-layer analogy

  • The mixing layer is the turbulence shear flow formed between two coflowing streams with different velocities.

  • The characteristic of the mixing layer is a strong inflection in the mean velocity profile.

  • Mixing layer turbulence has a distinctive pattern of coherent motion. It has streamwise periodicity, which is proportional to the vorticity thickness. The ratio ranges 3.5 to 5.

  • Turbulence depends on depth and friction velocity and is sensitive to initial conditions.


The mixing layer1
The Mixing Layer mixing-layer analogy


The canopy
The Canopy mixing-layer analogy


The conopy
The Conopy mixing-layer analogy


The canopy1

Eddies dominating turbulence transfer are of canopy scale. mixing-layer analogy

Three types of observations:

Honami waves

Two-point turbulence statistics

Conditional analyses

The Canopy


The mixing layer analogy
The Mixing-Layer Analogy mixing-layer analogy


The mixing layer anology
The Mixing-Layer Anology mixing-layer analogy


Conclusions
Conclusions mixing-layer analogy

  • Introduced basic properties of turbulence in canopies and in the mixing layer

  • Validated the mixing-layer analogy for the canopy by tests in three aspects: statistical flow properties, the turbulence energy budget and turbulent length scales

  • Described several useful statistical and observational methods in turbulence study


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