Using a One-and-a-Half Order Closure Model of the Atmospheric Boundary Layer for Surface Flux Footprint Estimation |
| |
Authors: | Andrey Sogachev Jon Lloyd |
| |
Institution: | (1) Max Planck Institute for Biogeochemistry, Postfach 10 01 64, 07701 Jena, Germany;(2) Department of Physical Sciences, University of Helsinki, P.O. Box 64, FIN-00014, Finland |
| |
Abstract: | A knowledge of the distribution of the contribution of upwind sources to measurements of vertical scalar flux densities is
important for the correct interpretation of eddy covariance data. Several approaches have been developed to estimate this
so-called footprint function. Here a new approach based on the ensemble-averaged Navier—Stokes equations is presented. Comparisons
of numerical results using this approach with results from other studies under a range of environmental conditions show that
the model predictions are robust. Moreover, the approach outlined here has the advantage of a potential wide applicability,
due to an ability to take into account the heterogeneous nature of underlying surfaces. For example, the model showed that
any variations in surface drag, such as must occur in real life heterogeneous canopies, can exert a marked influence of the
shape and extent of flux footprints. Indeed, it seems likely that under such circumstances, estimates of surface fluxes will
be weighted towards areas of highest foliage density (and therefore quite likely higher photosynthetic rates) close to the
measurement sensor.
Three-dimensional footprints during the day and night were also determined for a mixed coniferous forest in european Russia.
A marked asymmetry of the footprint in the crosswind direction was observed, this being especially pronounced for non-uniform
plant distributions involving vegetation types with different morphological and physiological properties. The model also found
that, other things being equal, the footprint peak for forest soil respiration is typically over twice the distance from the
above canopy measurement sensor compared to that for canopy photosynthesis. This result has important consequences for the
interpretation of annual ecosystem carbon balances by the eddy covariance method. |
| |
Keywords: | Ensemble-averaged model Flux footprint prediction Forest Heterogeneous canopies |
本文献已被 SpringerLink 等数据库收录! |
|