Advertisement

Advances in Atmospheric Sciences

, Volume 26, Issue 1, pp 9–16 | Cite as

A re-examination of density effects in eddy covariance measurements of CO2 fluxes

Article

Abstract

Corrections of density effects resulting from air-parcel expansion/compression are important in interpreting eddy covariance fluxes of water vapor and CO2 when open-path systems are used. To account for these effects, mean vertical velocity and perturbation of the density of dry air are two critical parameters in treating those physical processes responsible for density variations. Based on various underlying assumptions, different studies have obtained different formulas for the mean vertical velocity and perturbation of the density of dry air, leading to a number of approaches to correct density effects. In this study, we reexamine physical processes related to different assumptions that are made to formulate the density effects. Specifically, we re-examine the assumptions of a zero dry air flux and a zero moist air flux in the surface layer, used for treating density variations, and their implications for correcting density effects. It is found that physical processes in relation to the assumption of a zero dry air flux account for the influence of dry air expansion/compression on density variations. Meanwhile, physical processes in relation to the assumption of a zero moist air flux account for the influence of moist air expansion/compression on density variations. In this study, we also re-examine mixing ratio issues. Our results indicate that the assumption of a zero dry air flux favors the use of the mixing ratio relative to dry air, while the assumption of a zero moist air flux favors the use of the mixing ratio relative to the total moist air. Additionally, we compare different formula for the mean vertical velocity, generated by air-parcel expansion/compression, and for density effect corrections using eddy covariance data measured over three boreal ecosystems.

Key words

eddy covariance flux of CO2 flux correction density effects air-parcel expansion/compression open-path CO2/H2O infrared gas analyzer 

Preview

Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.

References

  1. Bakan, S., 1978: Note on the eddy correlation method for CO2 flux measurements. Bound.-Layer Meteor., 14, 597–600.CrossRefGoogle Scholar
  2. Baldocchi, D., J. Finnigan, K. Wilson, K. T. Paw U, and E. Falge, 2000: On measuring net ecosystem carbon exchange over tall vegetation on complex terrain. Bound.-Layer Meteor., 96, 257–291.CrossRefGoogle Scholar
  3. Baldocchi, D. D., and Coauthors, 2001: FLUXNET: A new tool to study the temporal and spatial variability of ecosystem-scale carbon dioxide, water vapor and energy flux densities. Bull. Amer. Meteor. Soc., 82, 2415–2435.CrossRefGoogle Scholar
  4. Bernhardt, K., and H. Piazena, 1988: Zum einfluss turbulenzbedingter dichteschwankungen auf die bestimmung turbulenter austauschstrome in der bodenschicht. Z. Meteorol., 38, 234–245.Google Scholar
  5. Brook, R. R., 1978: The influence of water vapor fluctuations on turbulent fluxes. Bound.-Layer Meteor., 15, 481–487.CrossRefGoogle Scholar
  6. Fuehrer, P. L., and C. A. Friehe, 2002: Flux corrections revisited. Bound.-Layer Meteor., 102, 415–457.CrossRefGoogle Scholar
  7. Jones, E. P., and S. D. Smith, 1978: The air density correction to eddy flux measurements. Bound.-Layer Meteor., 15, 357–360.CrossRefGoogle Scholar
  8. Kowalski, A. S., 2006a: Comment on “An Alternative Approach for CO2 Flux Correction Caused by Heat and Water Vapour Transfer” by Liu. Bound.-Layer Meteor., DOI 10.1007/s10546-005-9044-2.Google Scholar
  9. Kowalski, A. S., 2006b: Further comment on “Reply to The Comment by Kowalski on “An Alternative Approach for CO2 Flux Correction Caused by Heat and Water Vapour Transfer” by Liu”. Bound.-Layer Meteor., DOI 10.1007/s10546-006-9051-y.Google Scholar
  10. Lee, X., W. J. Massman, and B. Law, 2004: Handbook of Micrometeorology: A Guide for Surface Flux Mea surement and Analysis. Kluwer Academic Publishers, Dordrecht, 250pp.Google Scholar
  11. Leuning, R., 2004: Measurements of trace gas fluxes in the atmosphere using eddy covariance: WPL corrections revisited. Handbook of Micrometeorology: A Guide for Surface Flux Measurement and Analysis, Lee et al., Eds., Kluwer Academic Publishers, Dordrecht, 119–132.Google Scholar
  12. Leuning, R., 2007: The correct form of the Webb, Pearman and Leuning equation for eddy fluxes of trace gases in steady and non-steady state, horizontally homogeneous flows. Bound.-Layer Meteor., 123, 263–267.CrossRefGoogle Scholar
  13. Leuning, R., O. T. Denmead, and A. R. G. Lang, 1982: Effects of heat and water vapor transport on eddy covariance measurement of CO2 fluxes. Bound.-Layer Meteor., 23, 209–222.CrossRefGoogle Scholar
  14. Liebethal, C., and T. Foken, 2003: On the significance of the Webb correction to fluxes. Bound.-Layer Meteor., 109, 99–106.CrossRefGoogle Scholar
  15. Liebethal, C., and T. Foken, 2004: On the significance of the Webb correction to fluxes, Corrigendum. Bound.-Layer Meteor., 113, 301.CrossRefGoogle Scholar
  16. Liu, H. P., 2005: An alternative approach for CO2 flux correction caused by heat and water vapor transfer. Bound.-Layer Meteor., 115, 151–168.CrossRefGoogle Scholar
  17. Liu, H. P., 2006: Reply to the comment by Kowalski on “An Alternative Approach for CO2 Flux Correction Caused by Heat and Water Vapour Transfer”. Bound.-Layer Meteor., DOI 10.1007/s10546-005-9042-4.Google Scholar
  18. Liu, H. P., J. T. Randerson, J. Lindfors, and F. S. Chapin III, 2005: Changes in the surface energy budget after fire in boreal ecosystems of interior Alaska: An annual perspective. J. Geophys. Res., 110, D13101, doi:10.1029/2004JD005158.Google Scholar
  19. Massman, W. J., 2004: Concerning the measurement of atmospheric trace gas fluxes with open- and closed-path eddy covariance system: The WPL terms and spectral attenuation. Handbook of Micrometeorology: A Guide for Surface Flux Measurement and Analysis, Lee et al., eds., Kluwer Academic Publishers, Dordrecht, 133–160.Google Scholar
  20. Massman, W. J., and X. Lee, 2002: Eddy covariance flux corrections and uncertainties in long term studies of carbon and energy exchange. Agricultural and Forest Meteorology, 113, 121–144.CrossRefGoogle Scholar
  21. Massman, W. J., and J.-P. Tuovinen, 2006: An analysis and implications of alternative methods of deriving the density (WPL) terms for eddy covariance flux measurements. Bound.-Layer Meteor., 17, 375–379.Google Scholar
  22. Paw U, K. T., D. D. Baldocchi, T. P. Meyers, and K. E. Wilson, 2000: Correction of eddy-covariance measurements incorporating both advective effects and density fluxes. Bound.-Layer Meteor., 97, 487–511.CrossRefGoogle Scholar
  23. Reinking, R. F., 1980: The respective effects of water vapor and temperature on the turbulent fluxes of sensible and latent heat. Bound.-Layer Meteor., 19, 373–385.CrossRefGoogle Scholar
  24. Smith, S. D., and E. P. Jones, 1979: Dry-air boundary conditions for correction of eddy flux measurements. Bound.-Layer Meteor., 17, 375–379.CrossRefGoogle Scholar
  25. Sun, J., S. K. Esbensen, and L. Mahrt, 1995: Estimation of sensible heat flux. J. Atmos. Sci., 52, 3162–3171.CrossRefGoogle Scholar
  26. Webb, E. K., and G. I. Pearman, 1977: Correction of CO2 transfer measurements for the effect of water vapor transfer. Second Australasian Conference on Heat and Mass Transfer, University of Sydney, 469–476.Google Scholar
  27. Webb, E. K., G. I. Pearman, and R. Leuning, 1980: Correction of flux measurements for density effects due to heat and water vapor transfer. Quart. J. Roy. Meteor. Soc., 106, 85–100.CrossRefGoogle Scholar

Copyright information

© Chinese National Committee for International Association of Meteorology and Atmospheric Sciences, Institute of Atmospheric Physics, Science Press and Springer-Verlag GmbH 2009

Authors and Affiliations

  1. 1.Department of Physics, Atmospheric Sciences & GeoscienceJackson State UniversityJacksonUSA

Personalised recommendations