, Volume 67, Issue 3, pp 293318
First online:
Source areas for scalars and scalar fluxes
 H. P. SchmidAffiliated withDivision of Climate Research, Dept. of Geography, Swiss Federal Institute of Technology
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The spatial resolution of meteorological observations of scalars (such as concentrations or temperature) and scalar fluxes (e.g., watervapour flux, sensible heat flux) above inhomogeneous surfaces is in general not known. It is determined by the surface area of influence orsource area of the sensor, which for sensors of quantities that are subject to turbulent diffusion, depends on the flow and turbulence conditions.
Functions describing the relationship between the spatial distribution of surface sources (or sinks) and a measured signal at height in the surface layer have been termed thefootprint function or thesource weight function. In this paper, the source area of levelP is defined as the integral of the source weight function over the smallest possible domain comprising the fractionP of the total surface influence reflected in the measured signal. Source area models for scalar concentration and for passive scalar fluxes are presented. The results of the models are presented as characteristic dimensions of theP=50% source areas (i.e., the area responsible for 50% of the surface influence): the maximum source location (i.e., the upwind distance of the surface element with the maximumweight influence), the near and the far end of the source area, and its maximal lateral extension. These numerical model results are related directly to nondimensional surfacelayer scaling variables by a nonlinear least squares method in a parameterized model which provides a userfriendly estimate of the surface area responsible for measured concentrations or fluxes. The source area models presented here allow conclusions to be made about the spatial representativeness and the localness (these terms are defined in the text) of flux and concentration measurements.
 Title
 Source areas for scalars and scalar fluxes
 Journal

BoundaryLayer Meteorology
Volume 67, Issue 3 , pp 293318
 Cover Date
 199401
 DOI
 10.1007/BF00713146
 Print ISSN
 00068314
 Online ISSN
 15731472
 Publisher
 Kluwer Academic Publishers
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 Authors

 H. P. Schmid ^{(1)}
 Author Affiliations

 1. Division of Climate Research, Dept. of Geography, Swiss Federal Institute of Technology, Zürich, Switzerland