A Simple Parameterisation for Flux Footprint Predictions |
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Authors: | N Kljun P Calanca M W Rotach H P Schmid |
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Institution: | (1) Institute for Atmospheric and Climate Science ETH, Zurich, Switzerland;(2) Swiss Federal Research Station for Agroecology and Agriculture, Zurich, Switzerland;(3) Institute for Atmospheric and Climate Science ETH, Zurich, Switzerland;(4) Department of Geography, Bloomington, U.S.A.;(5) Present address: Swiss Federal Office of Meteorology and Climatology, MeteoSwiss, Zurich, Zurich |
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Abstract: | Flux footprint functions estimate the location and relative importance of passive scalar sources influencing flux measurements
at a given receptor height. These footprint estimates strongly vary in size, depending on receptor height, atmospheric stability,
and surface roughness. Reliable footprint calculations from, e.g., Lagrangian stochastic models or large-eddy simulations
are computationally expensive and cannot readily be computed for long-term observational programs. To facilitate more accessible
footprint estimates, a scaling procedure is introduced for flux footprint functions over a range of stratifications from convective
to stable, and receptor heights ranging from near the surface to the middle of the boundary layer. It is shown that, when
applying this scaling procedure, footprint estimates collapse to an ensemble of similar curves. A simple parameterisation
for the scaled footprint estimates is presented. This parameterisation accounts for the influence of the roughness length
on the footprint and allows for a quick but precise algebraic footprint estimation. |
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Keywords: | Boundary-layer scaling Boundary-layer stability Fetch Flux footprint Lagrangian stochastic particle dispersion model Parameterisation |
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