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Forest wind regimes and their implications on cross-canopy coupling

Title data

Freundorfer, Anita ; Rehberg, Ingo ; Law, Beverly E. ; Thomas, Christoph:
Forest wind regimes and their implications on cross-canopy coupling.
In: Agricultural and Forest Meteorology. Vol. 279 (15 December 2019) . - Art.Nr. 107696.
ISSN 0168-1923
DOI: https://doi.org/10.1016/j.agrformet.2019.107696

Abstract in another language

An analysis of wind regimes across forests of varying density and height is presented. The hockey stick-like dependence of the friction velocity on the mean advective wind speed is used to determine the threshold between the weak-wind and the strong-wind regime for the entire canopy. Such thresholds are compared across four different sites. The height dependence of thresholds within the canopy is inverted compared to the one above grassland sites. This can be understood by extending the accepted interpretation for weak-wind thresholds from grassland sites to forested sites.

Even for large fluctuations above the canopy, the fluctuations of the vertical wind velocity in the subcanopy remain small during weak-wind situations. Correspondingly, in the strong-wind regime, turbulence in the subcanopy remains strong in spite of reduced above-canopy turbulence. This fact suggests that previously used methods for determining the degree of coupling across the canopy layer based upon the ratio of the vertical wind variance between the above-canopy and subcanopy may prove erroneous. Furthermore, it emphasizes the significance of mechanisms generating subcanopy turbulence other than above-canopy turbulent transport and shear.

The transport of mass and energy between the subcanopy and above-canopy layers is significantly reduced during the weak-wind regime. In particular, the vertical turbulent transport is reduced by more than one order of magnitude. This suggests a decoupling of the subcanopy layer during weak-wind situations and allows for the accumulation of carbon dioxide originating from soil respiration in the subcanopy layer during the weak-wind regime.

Further data

Item Type: Article in a journal
Refereed: Yes
Keywords: Weak-wind; Turbulent transport; Decoupling; Subcanopy; Turbulence kinetic energy
Institutions of the University: Faculties > Faculty of Mathematics, Physics und Computer Science > Department of Physics > Chair Experimental Physics V > Chair Experimental Physics V - Univ.-Prof. Dr. Ingo Rehberg
Faculties > Faculty of Biology, Chemistry and Earth Sciences > Department of Earth Sciences > Professorship Micrometeorology > Professorship Micrometeorology - Univ.-Prof. Dr. Christoph K. Thomas
Profile Fields > Advanced Fields > Nonlinear Dynamics
Result of work at the UBT: Yes
DDC Subjects: 500 Science > 530 Physics
500 Science > 550 Earth sciences, geology
Date Deposited: 15 Oct 2019 07:55
Last Modified: 15 Oct 2019 07:55
URI: https://eref.uni-bayreuth.de/id/eprint/52758