Boundary‐layer flow within and above a forest canopy of variable density

Abstract

An analytical model is developed for flow within and above a forest canopy with a slowly varying canopy density. Results are compared with existing analytical models for flow over a surface with slowly varying roughness length, and also with numerical simulations. The results show that the analytical solution is successful in capturing the behaviour of the flow for small and slowly changing variations in canopy density. Previous models which only vary the roughness length and neglect changes in displacement height fail to capture the near-surface flow accurately. Including changes in displacement height as well as roughness length changes gives results closer to those obtained with the full canopy model, but even then the flow induced in the canopy leads to significant differences. The analytical model also highlights the sensitivity of the results to the parametrization of the vertical component of the turbulent stress tensor, τ zz . For shorter wavelength variations in the canopy density, the analytical model breaks down as the more rapid changes in density induce larger flow perturbations which lead to increased flow into and out of the canopy. This kind of idealised analytical study provides important insights into the role of canopy heterogeneities on boundary-layer flow. This is important both for understanding near-surface winds and transport, and also for parametrizing the effects of surface heterogeneities in large-scale weather and climate models.

A voxel-based approach for canopy structure characterization using full-waveform airborne laser scanning

“…Leiterer (1) , F. Morsdorf (1) , H. Torabzadeh (1) , M.E. Schaepman (1) , W. Mücke (2) , N. Pfeifer (2) , M. Hollaus (2) (1) Remote Sensing Laboratories, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland, Email: reik.leiterer, felix.morsdorf, hossein.torabzadeh, michael.schaepman@geo.uzh.ch (2) Institute of Photogrammetry and Remote Sensing, Vienna University of Technology, Gusshausstrasse 27-29, 1040 Vienna, Austria, Email: wm, np, mh@ipf.tuwien.ac.at…”

“…Leiterer (1) , F. Morsdorf (1) , H. Torabzadeh (1) , M.E. Schaepman (1) , W. Mücke (2) , N. Pfeifer (2) , M. Hollaus (2) ( …”

First‐order turbulence closure for modelling complex canopy flows

“…Then we review whether the closure schemes employed by two groups of models-mixing length closures eg. Finnigan and Belcher (2004) or Ross (2012) and the velocity-squared closure eg Yi et al (2005Yi et al ( , 2008-satisfy these requirements and illustrate how failure to do so can lead to incorrect results or inferences.…”

“…To understand these complex canopy flows at a fundamental level there is a need for simple (first-order) flow and transport models that allow analytic solutions or simple numerical computations that are not opaque Ôblack boxesÕ (e.g. Belcher et al, 2003;Finnigan and Belcher, 2004;Yi et al, 2005;Katul et al, 2006;Yi, 2008;Ross, 2012). It is important that the fluid mechanical principles underpinning such models be sound as the community increasingly relies on them for data interpretation.…”

Modelling Canopy Flows over Complex Terrain

“…Numerical simulations were conducted using the BLASIUS model, originally de-114 veloped at the UK Met Office and described in Wood and Mason (1993 (Ross, 2012). The model has been validated against 122 wind tunnel measurements over a hill, and against observations from a flat hetero-123 geneous forest (Ross and Vosper, 2005), but this is the first time the model has been 124 applied to such complex, heterogeneous terrain as this.…”