Boundary-Layer Meteorology

, Volume 91, Issue 2, pp 259–280 | Cite as

Autoregressive filtering versus linear detrending in estimation of fluxes by the eddy covariance method

  • Üllar Rannik
  • Timo Vesala
Article

Abstract

The application of autoregressive running mean filtering (RMF) and linear detrending (LDT) in the estimation of turbulent fluxes by the eddy covariance method is analysed. The systematic, as well as the random, errors of the fluxes arising from filtering and/or limited observation time effects are described. To observe negligible systematic errors in fluxes, the RMF has to be applied with moderately long time constants. However, the obtained flux values are subject to increased random errors during periods of non-stationarity and the method leads to systematic overestimation of variances. These shortcomings are not inherent in the LDT approach, which is recommended for use. But the systematic errors of fluxes due to LDT are not negligible under certain experimental conditions and have to be accounted for. The corrections are important because the relatively small errors in short-period fluxes can translate to significant errors in long-period averages. The corrections depend on the turbulence time scales, which should be preferably estimated as ensemble mean variables for a particular site.

Turbulent fluxes Filtering Linear detrending Eddy covariance method 

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References

  1. Foken, Th. and Wichura, B.: 1996, ‘Tools for Quality Assessment of Surface-Based Flux Measurements', Agric. For. Meteorol. 78, 83-105.Google Scholar
  2. Gash, J. H. C. and Culf, A. D.: 1996, ‘Applying a Linear Detrend to Eddy Correlation Data in Real Time', Boundary-Layer Meteorol. 79, 301-306.Google Scholar
  3. Horst, T. W.: 1997, ‘A Simple Formula for Attenuation of Eddy Fluxes Measured with First-Order-Response Scalar Sensors', Boundary-Layer Meteorol. 82, 219-233.Google Scholar
  4. Kaimal, J. C. and Finnigan, J. J.: 1994, Atmospheric Boundary Layer Flows. Their Structure and Measurement, Oxford University Press, New York, 289 pp.Google Scholar
  5. Kaimal, J. C., Wyngaard, J. C., Izumi, Y., and Cote, O. R.: 1972, ‘Spectral Characteristics of Surface-Layer Turbulence', Quart. J. Roy. Meteorol. Soc. 98, 563-589.Google Scholar
  6. Kristensen, L.: 1998, Time Series Analysis. Dealing with Imperfect Data, Risø National Laboratory, Risø-I-1228(EN), 31 pp.Google Scholar
  7. Lee, X.: 1996, ‘Turbulence Spectra and Eddy Diffusivity over Forests', J. Appl. Meteorol. 35, 1307-1318.Google Scholar
  8. Lee, X.: 1998, ‘On Micrometeorological Observations of Surface-Air Exchange over Tall Vegetation', Agric. For. Meteorol. 91, 39-49.Google Scholar
  9. Lenschow, D. H. and Kristensen, L.: 1985, ‘Uncorrelated Noise in Turbulence Measurements', J. Atmos. Oceanic Tech. 2, 68-81.Google Scholar
  10. Lenschow, D. H., Mann, J., and Kristensen, L.: 1994, ‘How Long Is Long Enough when Measuring Fluxes and Other Turbulence Statistics?', J. Atmos. Oceanic Tech. 18, 661-673.Google Scholar
  11. McMillen, R. T.: 1988, ‘An Eddy Correlation Technique with Extended Applicability to Non-Simple Terrain', Boundary-Layer Meteorol. 43, 231-245.Google Scholar
  12. Moncrieff, J. B., Massheder, J. M., De Bruin, H., Elbers, J., Friborg, T., Huesunkveld, B., Kabat, P., Scott, S., Soegaard, H., and Verhoef, A.: 1997, ‘A System to Measure Surface Fluxes of Momentum, Sensible Heat, Water Vapour and Carbon Dioxide', J. Hydrol. 189, 589-611.Google Scholar
  13. Monin, A. S. and Yaglom, A. M.: 1971, Statistical Fluid Mechanics, Vol. 1, MIT Press, 769 pp.Google Scholar
  14. Moore, C. J.: 1986, ‘Frequency Response Corrections for Eddy Correlation Systems', Boundary-Layer Meteorol. 37, 17-35.Google Scholar
  15. Rannik, Ü.: 1998, ‘On the Surface Layer Similarity at a Complex Forest Site', J. Geophys. Res. 103, 8685-8697.Google Scholar
  16. Shuttleworth, W. J.: 1980, ‘Corrections for the Effect of Background Concentration Change and Sensor Drift in Real-Time Eddy Correlation Systems', Boundary-Layer Meteorol. 42, 167-180.Google Scholar
  17. Webb, E. K., Pearman, G. I., and Leuning, R.: 1980, ‘Correction of Flux Measurements for Density Effects Due To Heat and Water Vapour Transfer', Quart. J. Roy. Meteorol. Soc. 106, 85-100.Google Scholar

Copyright information

© Kluwer Academic Publishers 1999

Authors and Affiliations

  • Üllar Rannik
    • 1
  • Timo Vesala
    • 1
  1. 1.Department of PhysicsUniversity of HelsinskiHelsinskiFinland

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