Observations of the scale-dependent turbulence and evaluation of the flux-gradient relationship for sensible heat for a closed Douglas-fir canopy in very weak wind conditions Public Deposited

http://ir.library.oregonstate.edu/concern/articles/z316q3523

This is the publisher’s final pdf. The published article is copyrighted by the author(s) and published by Copernicus Publications on behalf of the European Geosciences Union. The published article can be found at:  http://www.atmospheric-chemistry-and-physics.net/home.html.

Descriptions

Attribute NameValues
Creator
Abstract or Summary
  • Observations of the scale-dependent turbulent fluxes, variances, and the bulk transfer parameterization for sensible heat above, within, and beneath a tall closed Douglas-fir canopy in very weak winds are examined. The daytime sub-canopy vertical velocity spectra exhibit a double-peak structure with peaks at timescales of 0.8 s and 51.2 s. A double-peak structure is also observed in the daytime sub-canopy heat flux co-spectra. The daytime momentum flux co-spectra in the upper bole space and in the sub-canopy are characterized by a relatively large crosswind component, likely due to the extremely light and variable winds, such that the definition of a mean wind direction, and subsequent partitioning of the momentum flux into along- and cross-wind components, has little physical meaning. Positive values of both momentum flux components in the sub-canopy contribute to upward transfer of momentum, consistent with the observed sub-canopy secondary wind speed maximum. For the smallest resolved scales in the canopy at nighttime, we find increasing vertical velocity variance with decreasing timescale, consistent with very small eddies possibly generated by wake shedding from the canopy elements that transport momentum, but not heat. Unusually large values of the velocity aspect ratio within the canopy were observed, consistent with enhanced suppression of the horizontal wind components compared to the vertical by the very dense canopy. The flux–gradient approach for sensible heat flux is found to be valid for the sub-canopy and above-canopy layers when considered separately in spite of the very small fluxes on the order of a few Wm⁻² in the sub-canopy. However, single-source approaches that ignore the canopy fail because they make the heat flux appear to be counter-gradient when in fact it is aligned with the local temperature gradient in both the sub-canopy and above-canopy layers. While sub-canopy Stanton numbers agreed well with values typically reported in the literature, our estimates for the above-canopy Stanton number were much larger, which likely leads to underestimated modeled sensible heat fluxes above dark warm closed canopies.
Resource Type
DOI
Date Available
Date Issued
Citation
  • Vickers, D., & Thomas, C. K. (2014). Observations of the scale-dependent turbulence and evaluation of the flux-gradient relationship for sensible heat for a closed Douglas-Fir canopy in very weak wind conditions. Atmospheric Chemistry and Physics, 14(18), 9665-9676. doi:10.5194/acp-14-9665-2014
Series
Rights Statement
Funding Statement (additional comments about funding)
Publisher
Peer Reviewed
Language
Replaces
Additional Information
  • description.provenance : Submitted by Erin Clark (erin.clark@oregonstate.edu) on 2014-10-17T18:55:05Z No. of bitstreams: 2 license_rdf: 1370 bytes, checksum: cd1af5ab51bcc7a5280cf305303530e9 (MD5) VickersDeanCEOASObservationsScale-Dependent.pdf: 720071 bytes, checksum: 527265c1485131787b2ad6151f6513d3 (MD5)
  • description.provenance : Made available in DSpace on 2014-10-17T18:55:23Z (GMT). No. of bitstreams: 2 license_rdf: 1370 bytes, checksum: cd1af5ab51bcc7a5280cf305303530e9 (MD5) VickersDeanCEOASObservationsScale-Dependent.pdf: 720071 bytes, checksum: 527265c1485131787b2ad6151f6513d3 (MD5) Previous issue date: 2014-09-16
  • description.provenance : Approved for entry into archive by Erin Clark(erin.clark@oregonstate.edu) on 2014-10-17T18:55:23Z (GMT) No. of bitstreams: 2 license_rdf: 1370 bytes, checksum: cd1af5ab51bcc7a5280cf305303530e9 (MD5) VickersDeanCEOASObservationsScale-Dependent.pdf: 720071 bytes, checksum: 527265c1485131787b2ad6151f6513d3 (MD5)

Relationships

In Administrative Set:
Last modified: 07/26/2017

Downloadable Content

Download PDF
Citations:

EndNote | Zotero | Mendeley

Items