Datensatz

Zusammenfassung

Measuring turbulent fluxes with the eddy covariance method has\par become a widely accepted and powerful tool for the determination of\par long term data sets for the exchange of momentum, sensible and\par latent heat, and trace gases such as CO₂ between the atmosphere and\par the underlying surface. Several flux networks developed continuous\par measurements above complex terrain, e.g. AmeriFlUx and EUROFLUX,\par with a strong focus on the net exchange of CO₂ between the\par atmosphere and the underlying surface. Under many conditions basic\par assumptions for the eddy covariance method in its simplified form,\par such as stationarity of the flow, homogeneity of the surface and\par fully developed turbulence of the flow field, are not fulfilled. To\par deal with non-ideal conditions which are common at many FLUXNET\par sites, quality tests have been developed to check if these basic\par theoretical assumptions are valid.\par tests described by Foken and Wichura (1996) with the analytical\par footprint model of Schmid (1997). The aim was to identify suitable\par wind sectors and meteorological conditions for flux measurements.\par These tools were used on data of 18 participating sites. Quality\par tests were applied on the fluxes of momentum, sensible and latent\par heat, and on the CO₂-flux, respectively. The influence of the\par topography on the vertical wind component was also checked. At many\par sites the land use around the flux towers is not homogeneous or the\par fetch may not be large enough. So the relative contribution of the\par land use type intended to be measured was also investigated. Thus\par the developed tool allows comparative investigations of the measured\par turbulent fluxes at different sites if using the same technique and\par algorithms for the determination of the fluxes as well as analyses\par of potential problems caused by influences of the surrounding land\par use patterns. [References: 51]\par