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Flux‐gradient relationships for momentum and heat over a rough natural surface
Author(s) -
Fazu Chen,
Schwerdtfeger Peter
Publication year - 1989
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.49711548607
Subject(s) - turbulence , eddy , heat flux , momentum (technical analysis) , heat transfer , momentum transfer , flux (metallurgy) , atmospheric sciences , sensible heat , temperature gradient , canopy , instability , physics , mechanics , meteorology , materials science , optics , geography , finance , archaeology , scattering , economics , metallurgy
The flux‐gradient relationships for momentum and heat have been investigated over extensive flat bushland ( h = 2.3 m, z o = 0.4 m) with observations being made at several levels extending up to 10 times the canopy height. It has been found that: (1) Eddy diffusivities for momentum and heat, K H and K M , are enhanced by factors of 1.65 and 2.5 respectively under near‐neutral conditions and within the layer close to the canopy. (2) These enhancements distinctly depend on instability, and their variations with height are not simply monotonic, as expected in earlier investigations. (3) Even a counter‐gradient flux of heat could occur under some circumstances. (4) The level of enhancement remains substantially unchanged over different surfaces for heat transfer but decreases as the canopy density increases in the case of momentum transfer. Possible mechanisms are discussed. (5) The length scale of atmospheric turbulence should be taken into account in studies of turbulent transfer over very rough surfaces, where the large‐scale eddies may have a key role.