Abstract
The flux footprint is the contribution, per unit emission, of each element of a surface area source to the vertical scalar flux measured at height z m ; it is equal to the vertical flux from a unit surface point source. The dependence of the flux footprint on crosswind location is shown to be identical to the crosswind concentration distribution for a unit surface point source; an analytic dispersion model is used to estimate the crosswind-integrated flux footprint. Based on the analytic dispersion model, a normalized crosswind-integrated footprint is proposed that principally depends on the single variable z/z m , where z is a measure of vertical dispersion from a surface source. The explicit dependence of the crosswind-integrated flux footprint on downwind distance, thermal stability and surface roughness is contained in the dependence of z on these variables. By also calculating the flux footprint with a Lagrangian stochastic dispersion model, it is shown that the normalized flux footprint is insensitive to the analytic model assumption of a self-similar vertical concentration profile.
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The National Center for Atmospheric Research is funded by the National Science Foundation.
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Horst, T.W., Weil, J.C. Footprint estimation for scalar flux measurements in the atmospheric surface layer. Boundary-Layer Meteorol 59, 279–296 (1992). https://doi.org/10.1007/BF00119817
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DOI: https://doi.org/10.1007/BF00119817