Use of footprint modelling for the characterisation of complex meteorological flux measurement sites
Abstract
A tool for the evaluation of complex flux measurement sites has been developed which combines existing quality assessment tools for flux measurements with footprint modelling. In this way it is possible to define the spatial context of the fluxes measured, and to include both topographical and land use features of the surrounding terrain and micrometeorological flux data in the analysis. This approach allows us to determine the flux data quality for different wind sectors and meteorological conditions, and thus to identify the most suitable situations for the collection of high-quality data sets. To prepare the input data set for the quality assessment tool, data quality flags have to be assigned for the flux measurements and the source area has to be calculated. The quality flag assignment adopted within this program is based on FOKEN &WICHURA (1996), while the footprint routine used in the actual version of the quality assessment software is the FSAM-model proposed by SCHMID (1997). To produce the overall performance of the flux data quality for a specific site, the results of those two analyses are combined. This process is termed source weight synthesis because the products of the procedure are two-dimensional matrices and graphs which form a combination of all the footprint analyses for the specific site. The software for this purpose, which was produced in the course of this quality assessment approach, is termed TERRAFEX. This software has been tested thoroughly within the frame of the CARBOEUROFLUX project and the German Program on Atmospheric research, AFO 2000, sub-project VERTIKO. The results can be provided in tabulated form or illustrated by 3-dimensional graphs, indicating the computed flux property for discrete grid cells in the area surrounding the tower. These graphs are routinely produced for - the flux contribution to the total flux. - the quality assessment of the fluxes of momentum, sensible heat, latent heat and CO2. - the vertical wind speed, with respect to the topography of the area. - the percentage of the land use type of interest. As an example the results for the Waldstein/Weidenbrunnen site in the Fichtelgebirge mountains near Bayreuth, Germany, will be presented.
- Publication:
-
EGS - AGU - EUG Joint Assembly
- Pub Date:
- April 2003
- Bibcode:
- 2003EAEJA.....2004G