A Perspective on Thirty Years of the Webb,Pearman and Leuning Density Corrections |
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| Authors: | Xuhui Lee William J Massman |
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| Institution: | (1) CSIRO Marine and Atmospheric Research, PO Box 1666, Canberra, ACT, 2601, Australia |
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| Abstract: | The density correction theory of Webb et al. (1980, Q J Roy Meteorol Soc 106: 85–100, hereafter WPL) is a principle underpinning the experimental investigation of surface fluxes
of energy and masses in the atmospheric boundary layer. It has a long-lasting influence in boundary-layer meteorology and
micrometeorology, and the year 2010 marks the 30th anniversary of the publication of the WPL theory. We provide here a critique
of the theory and review the research it has spurred over the last 30 years. In the authors’ opinion, the assumption of zero
air source at the surface is a fundamental novelty that gives the WPL theory its enduring vitality. Considerations of mass
conservation show that, in a non-steady state, the WPL mean vertical velocity and the thermal expansion velocity are two distinctly
different quantities of the flow. Furthermore, the integrated flux will suffer a systematic bias if the expansion velocity
is omitted or if the storage term is computed from time changes in the CO2 density. A discussion is provided on recent efforts to address several important practical issues omitted by the original
theory, including pressure correction, unintentional alternation of the sampled air, and error propagation. These refinement
efforts are motivated by the need for an unbiased assessment of the annual carbon budget in terrestrial ecosystems in the
global eddy flux network (FluxNet). |
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