Correction of flux measurements for density effects due to heat and water vapour transfer

Quarterly Journal of the Royal Meteorological Society - Tập 106 Số 447 - Trang 85-100 - 1980
E. K. Webb1, G. I. Pearman1, R. Leuning2
1CSIRO, Division of Atmospheric Physics, Aspendale, Victoria 3195, Australia
2Department of Land Resource Science, University of Guelph, Guelph, Ontario, N1G 2W1 Canada

Tóm tắt

AbstractWhen the atmospheric turbulent flux of a minor constituent such as CO2 (or of water vapour as a special case) is measured by either the eddy covariance or the mean gradient technique, account may need to be taken of variations of the constituent's density due to the presence of a flux of heat and/or water vapour. In this paper the basic relationships are discussed in the context of vertical transfer in the lower atmosphere, and the required corrections to the measured flux are derived.If the measurement involves sensing of the fluctuations or mean gradient of the constituent's mixing ratio relative to the dry air component, then no correction is required; while with sensing of the constituent's specific mass content relative to the total moist air, a correction arising from the water vapour flux only is required. Correspondingly, if in mean gradient measurements the constituent's density is measured in air from different heights which has been pre‐dried and brought to a common temperature, then again no correction is required; while if the original (moist) air itself is brought to a common temperature, then only a correction arising from the water vapour flux is required.If the constituent's density fluctuations or mean gradients are measured directly in the air in situ, then corrections arising from both heat and water vapour fluxes are required.These corrections will often be very important. That due to the heat flux is about five times as great as that due to an equal latent heat (water vapour) flux. In CO2 flux measurements the magnitude of the correction will commonly exceed that of the flux itself. The correction to measurements of water vapour flux will often be only a few per cent but will sometimes exceed 10 per cent.

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Quarterly Journal of the Royal Meteorological Society

Tập 106 Số 447

85-100

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