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Inverse Cascade Evidenced by Information Entropy of Passive Scalars in Submerged Canopy Flows
Author(s) -
Ghannam Khaled,
Poggi Davide,
BouZeid Elie,
Katul Gabriel G.
Publication year - 2020
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2020gl087486
Subject(s) - turbulence , cascade , physics , canopy , scalar (mathematics) , drag , wake , wavenumber , flume , scaling , inverse , mechanics , meteorology , geometry , optics , flow (mathematics) , mathematics , geography , chemistry , archaeology , chromatography
Turbulent mixing of scalars within canopies is investigated using a flume experiment with canopy‐like rods of height h mounted to the channel bed. The data comprised a time sequence of high‐resolution images of a dye recorded in a plane parallel to the bed at z / h = 0.2. Image processing shows that von Kármán wakes shed by canopy drag and downward turbulent transport from upper canopy layers impose distinct scaling regimes on the scalar spectrum. Measures from information theory are then used to explore the dominant directionality of the interaction between small and large scales underlying these two spectral regimes, showing that the arrival of sweeps from aloft establishes an inertial‐range spectrum with forward “information” cascade. In contrast, wake growth with downstream distance leads to persistent upscale transfer (inverse cascade) of scalar variance, which hints at their nondiffusive character and the significance of the stem diameter as an active length scale in canopy turbulence.