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Titel |
Multilevel Investigation of Subcanopy Respiration Flux by Relaxed Eddy Accumulation Conditional Sampling above and within a Spruce Forest |
VerfasserIn |
T. Gerken, A. Serafimovich, T. Foken |
Konferenz |
EGU General Assembly 2009
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 11 (2009) |
Datensatznummer |
250021674
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Zusammenfassung |
This work investigates the subcanopy respiration flux (Re), which reflects mainly CO2 soil
efflux, at the coniferous Weidenbrunnen FLUXNET site, located in the Fichtelgebirge
Mountains (Northern Bavaria) and is applying a recently developed Relaxed Eddy
Accumulation (REA) conditional sampling approach to high frequency eddy covariance data.
Data was collected within the framework of the EGER (ExchanGE processes in
mountainous Regions) project and during the first Intensive Observation Period (IOP1).
The project is focused on the detailed quantification of relevant processes within
the soil-vegetation-atmosphere system by observing diurnal and annual cycles of
energy, water and trace gases. Five days were selected from IOP1 (20.09.2007
to 24.09.2007) and high frequency times series of wind vector , water vapor and
CO2 were recorded at five sampling heights below, within and above the forest
canopy.
Eddies transporting respiration flux information from the ground to the air above the
canopy are considered to possess a unique and detectable CO2 and water vapor signature.
Due to the characteristic vertical profiles of CO2 and water vapor concentrations, they are
enriched in CO2 and water vapor compared to the mean concentrations measured above the
canopy. The method used is based on the assumption that these eddies are transported past the
sensor levels without being altered by surrounding eddies. It combines REA with hyperbolic
dead bands and quadrant analysis, extracting the respiration events from the overall dataset.
The overall REA formulation and its statistics were checked. The REA method is likely to
overestimate fluxes due to overestimation of the β- coefficient used in relaxed eddy
accumulation approaches. Re- events were identified and extracted from the data with
hyperbolic thresholds of H = 0.25 and 0.5. For daytime conditions and above canopy
systems the results were in the same order of magnitude to expected respiration fluxes, with
H = 0.5 yielding best results. The estimates at the below canopy systems and during
nighttime conditions were too large. The time fraction of daytime respiration events was |
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