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Flux profile relations above tall vegetation
Author(s) -
Garratt J. R.
Publication year - 1978
Publication title -
quarterly journal of the royal meteorological society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.744
H-Index - 143
eISSN - 1477-870X
pISSN - 0035-9009
DOI - 10.1002/qj.49710443915
Subject(s) - roughness length , stanton number , momentum transfer , surface roughness , flux (metallurgy) , momentum (technical analysis) , surface finish , surface (topology) , geometry , atmospheric sciences , meteorology , mathematics , physics , wind speed , turbulence , thermodynamics , materials science , wind profile power law , reynolds number , optics , finance , economics , scattering , metallurgy , composite material
Experimental data on the Monin and Obukhov functions, Φ M (ζ) and Φ H (ζ), obtained above an aerodynamically very rough surface (trees and shrubs, with z o , the aerodynamic roughness length, =0.4 m) in unstable conditions suggest they depend upon a nondimensional height ξ = z / z 0 . At the lowest height (ξ = 20), in neutral conditions, the inferred values of Φ M and Φ H (0) are 0.58 and 0.61 respectively, generally increasing as ξ increases to values not significantly different from unity at the greatest height (ξ = 85). Such values compare with the value unity found over ‘smooth’ surfaces at much greater values of ξ. This indicates that the depth of the transition layer for momentum transfer above this surface (=Z min , the minimum height of validity of the neutral logarithmic law) is given by Z mins ≈ 4.5 h , where h is the height of the main roughness elements; and for heat transfer Z min ≈3 h . The results suggest that eddy diffusivities are considerably greater just above tall vegetation than at corresponding heights above ‘smooth’ surfaces.