EGU2020-5506, updated on 27 Jun 2024
https://doi.org/10.5194/egusphere-egu2020-5506
EGU General Assembly 2020
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

Disentangling turbulent and non-diffusive fluxes in the boundary layer

Andrew Kowalski1,2, Gerardo Fratini3, Gabriela Miranda4, Penélope Serrano-Ortiz2,5, and George Burba3,6
Andrew Kowalski et al.
  • 1Universidad de Granada, Departamento de Física Aplicada, Granada, Spain
  • 2Andalusian Institute for Earth System Research (IISTA-CEAMA), Granada, Spain
  • 3LI-COR Biosciences, 4647 Superior St, Lincoln, Nebraska, USA
  • 4University of Wageningen, Wageningen, the Netherlands
  • 5Universidad de Granada, Departamento de Ecología, Granada, Spain
  • 6R.B. Daugherty Water for Food Global Institute, Bio-Atmospheric Sciences, School of Natural Resources, University of Nebraska, Lincoln, Nebraska, USA

Arithmetic averaging procedures are traditionally used in many applications in the field of micrometeorology, but these neglect Osborne Reynolds's specification of turbulence, and thus, strictly speaking, violate the momentum conservation law. Recently, it has been shown  that applying linear momentum conservation to surface exchanges defines an average motion in the surface-normal direction (i.e., a Stefan flow), and thereby describes a non-diffusive transport that is distinct from turbulent transport. Here we examine data from a nearly ideal micrometeorological field site (extensive, flat, and mono specific-reed wetland) to show that traditional flux-tower calculations, including but not limited to the Webb corrections,  generally provide an inadequate approximation of turbulent  fluxes and yet still adequately characterize the net fluxes in most traditional cases. The importance of such conflation of diffusive and non-diffusive transport is greatest for situations with relatively large non-diffusive fluxes, as occurs during particular times of day in general and particularly when considering fluxes in the stream-wise direction. An examination of fluxes calculated using the traditional arithmetic averaging procedure, versus the proposed, more theoretically appropriate calculations that fully obey conservation law, illustrates important implications for the characterization of gas-exchange processes and more generally the discipline of micrometeorology. These implications may become particularly critical in near future as gas flux measurements enter an era of automated operation on massive network scales, including automated gas flux calculations. At the same time, such measurements strive to adequately represent gas exchange of newer species with extremely low fluxes (vs traditionally measured larger fluxes of H2O and CO2). Multiple assumptions, and neglected terms and processes historically deployed for evaluating larger fluxes, may no longer work well when much smaller fluxes are considered, especially when measured by a non-expert using a fully automated flux station. These no-longer-negligible aspects include fundamentals of adequately handling the diffusive and non-diffusive transport mechanisms addressed in this presentation.

How to cite: Kowalski, A., Fratini, G., Miranda, G., Serrano-Ortiz, P., and Burba, G.: Disentangling turbulent and non-diffusive fluxes in the boundary layer, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5506, https://doi.org/10.5194/egusphere-egu2020-5506, 2020.

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