Arbeitsergebnisse / Universität Bayreuth, Abteilung Mikrometeorologie
3 search hits
- 52
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Jahresbericht 2010-11 zum Förderprojekt 01879 Untersuchung der Veränderung der Konzentration von Luftbeimengungen und Treibhausgasen im hohen Fichtelgebirge 2007 – 2014
(2012)
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Thomas Foken
Lisa Dirks
- no abstract
- 51
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Whole-air relaxed eddy accumulation for the measurement of isotope and trace-gas fluxes
(2012)
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Johannes Ruppert
Michael Riederer
Willi A. Brand
Thomas Foken
- Measuring the isotopic composition of trace gas fluxes can provide additional information on ecosystem gas exchange, when ecosystem processes, like assimilation, discriminate against heavier isotopes. In the case of CO2 exchange, different mass-balances for bulk CO2 and its 13CO2 or CO18O isotopes can be used to separate respiration from photosynthetic assimilation. Up to now, detectors for direct isotope measurements in the field lack the precision needed for fast eddy covariance (EC) flux measurements. The collection of updraft and downdraft whole-air samples using the relaxed eddy accumulation technique (REA) allows simultaneously determining trace gas concentrations and isotope ratios by high precision laboratory analysis. At the same time whole-air REA relaxes several of the technical problems related to REA sampling on traps. In tests using air from a tank the complete whole-air REA sampling system and its foil balloon bag reservoirs showed no signs of contamination after cleaning. The standard deviations of δ13C and δ18O isotope ratios were only slightly higher than the precision specified for the laboratory analysis procedure. First experiment results showed that isotopic differences (up-drafts−downdrafts) were large enough to yield signal to noise ratios greater than five when applying hyperbolic deadbands during REA sampling (HREA). The performance of the instrument and the HREA sampling method are investigated by simulation of the sampling process for bulk CO2, which serves as proxy scalar. Measurements by whole-air HREA in combination with high precision isotope analysis can quantify the isofluxes of 13CO2 and CO18O. Furthermore, additional information is collected on the scalar correlation of bulk CO2 and its stable isotopes, which represents the relatively short timescale of updrafts and downdrafts in the turbulent exchange above an ecosystem. This information is essential to check the scalar similarity assumptions made in the HREA and EC/flask method for the quan-tification of isofluxes.
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The Arctic Turbulence Experiment 2009 - additional laser Scintillometer measurement campaign 2009 at the Bayelva catchment on Svalbard: Technical documentation and visualization of the near surface measurements during the ARCTEX-2009 campaign, August, 10th to August, 20th 2009
(2012)
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Johannes Lüers
Jörg Bareiss
Martin Wagner
- Accurate quantification of turbulent fluxes between the surface and the atmospheric boundary layer in polar environments, characterized by frequent change of weather and exchange conditions (stable to very stable or intermittent; rapid, short term neutral to unstable stratified conditions) is a fundamental problem in soil-snow-ice-vegetation-atmosphere interaction processes. The observed rapid climate warming in the Arctic requires improvements in the permafrost and carbon cycle monitoring. To address these problems, it is essential to improve the databases with high-quality in-situ measurements of turbulent fluxes above tundra landscape surfaces applying the Eddy-Covariance method and the laser scintillometry. Results from the Arctic Turbulence Experiment 2006 on Svalbard helped to better understand physical exchange processes of energy and matter transport and to improve instrumentation standards as well as quality assessment techniques (Lüers and Bareiss 2010, 2011; http://www.arctex.uni-bayreuth.de). Therefore, the primary goal of this additional laser scintillometer measurement campaign is to estimate the flux contributions covering typical tundra surfaces across the Bayelva catchment during a summer season south-west of the Ny-Ålesund village, Kongsfjord, Svalbard. This effort makes it possible to define the spatial context of the fluxes, and to include land use features of the surrounding terrain in the quality assessment of all observations in the Bayelva catchment over the last 10 years performed by the Alfred Wegener Institute for Polar and Marine Research (AWI).
