caa a22 4500 475777344 CHVBK 20180406123634.0 cr unu---uuuuu 170329e20000101xx s 000 0 eng 10.1023/A:1002406616227 doi (NATIONALLICENCE)springer-10.1023/A:1002406616227 The Control Of Coherent Eddies In Vegetation Canopies: Streamwise Structure Spacing, Canopy Shear Scale And Atmospheric Stability [Elektronische Daten] [Y. Brunet, M. Irvine] An analogy has been established between a plane mixing layer and the atmospheric flow near the top of a vegetation canopy. It is based on a common feature, a strong inflection in the mean velocity profile, responsible for hydrodynamical instabilities that set the pattern for the coherent eddies and determine the turbulence length scales. In an earlier study, this analogy was tested using a small data set from thirteen experiments, all in near-neutral conditions. It provided a good prediction of the streamwise spacing Λw of the dominant canopy eddies (evaluated from time series of vertical velocity) that appears to depend on a shear length scale Ls = U(h)/U'(h), where h is canopy height, U is mean velocity and U' the vertical gradient dU/dz. The present analysis utilizes an extensive data set of approximately 700 thirty-minute runs, from six experiments on two forest sites and a maize crop, with a large range of stability conditions. Λw was estimated for each run using the wavelet transform as an objective, automated detection method. First, the variations of Λw and Ls with atmospheric stability are discussed. Neutral and unstable values exhibit a large scatter whereas in stable conditions both variables decrease with increasing stability. It is subsequently found that Λw is directly related to Ls, in a way close to the neutral prediction Λw /h = 8.1Ls/h.The Strouhal number Str = Ls /Λw is then shown to vary with atmospheric stability, weakly in unstable conditions, more significantly in stable conditions. Altogether these results suggest that, to some extent, the plane mixing-layer analogy can be extended to non-neutral conditions. It is argued that the primary effect of atmospheric stability, at least in stable conditions, is to modify the shear length scale Ls through changes in U(h) and U'(h), which in turn determines the streamwise spacing of the active, coherent motions. Kluwer Academic Publishers, 2000 Turbulence nationallicence Coherent eddies nationallicence Plant canopy nationallicence Plane mixing layer nationallicence Canopy shear scale nationallicence Atmospheric stability nationallicence Brunet Y. Unité de Bioclimatologie-INRA, BP 81, 33883, Villenave d'Ornon Cedex, France aut Irvine M. Unité de Bioclimatologie-INRA, BP 81, 33883, Villenave d'Ornon Cedex, France aut Boundary-Layer Meteorology Kluwer Academic Publishers 94/1(2000-01-01), 139-163 0006-8314 94:1<139 2000 94 10546 https://doi.org/10.1023/A:1002406616227 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1023/A:1002406616227 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Brunet Y. Unité de Bioclimatologie-INRA, BP 81, 33883, Villenave d'Ornon Cedex, France aut NATIONALLICENCE 700 1- Irvine M. Unité de Bioclimatologie-INRA, BP 81, 33883, Villenave d'Ornon Cedex, France aut NATIONALLICENCE 773 0- Boundary-Layer Meteorology Kluwer Academic Publishers 94/1(2000-01-01), 139-163 0006-8314 94:1<139 2000 94 10546 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer