Coherent eddies and turbulence in vegetation canopies: The mixing-layer analogy

摘要: This paper argues that the active turbulence and coherent motions near top of a vegetation canopy are patterned on plane mixing layer, because instabilities associated with characteristic strong inflection in mean velocity profile. Mixing-layer turbulence, formed around inflectional profile which develops between two coflowing streams different velocities, differs several ways from surface layer. Through these differences, mixing-layer analogy provides an explanation for many observed distinctive features turbulence. These include: (a) ratios components Reynolds stress tensor; (b) ratio K H /K M eddy diffusivities heat momentum; (c) relative roles ejections sweeps; (d) behaviour turbulent energy balance, particularly major role transport; (e) length scales (the dominant eddies responsible vertical transfer canopy). It is predicted controlled by shear scale L s = U(h)/U′(h) (where h height, U(z) as function height z, U′ dU/dz). In particular, streamwise spacing Λ x mL , m 8.1. predictions tested against sets field wind-tunnel data. We propose picture modulated larger-scale, inactive quasi-horizontal canopy.