Inverse Cascade Evidenced by Information Entropy of Passive Scalars in Submerged Canopy Flows

Khaled Ghannam, Davide Poggi, Elie Bou-Zeid, Gabriel G. Katul

Research output: Contribution to journalArticle

Abstract

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.

Original languageEnglish (US)
Article numbere2020GL087486
JournalGeophysical Research Letters
Volume47
Issue number9
DOIs
StatePublished - May 16 2020

All Science Journal Classification (ASJC) codes

  • Geophysics
  • Earth and Planetary Sciences(all)

Keywords

  • canopy turbulence
  • inverse cascade
  • land-atmosphere exchange
  • scalar mixing

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