References of "Kolle, Olaf"
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See detailChapter 3: Data Acquisition and Flux Calculations
Rebmann, Corinna; Kolle, Olaf; Heinesch, Bernard ULg et al

in Aubinet, Marc; Vesala, Timo; Papale, Dario (Eds.) Eddy Covariance: A Practical Guide to Measurement and Data Analysis (2012)

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See detailTreatment and assessment of the CO2-exchange at a complex forest site in Thuringia, Germany
Rebmann, Corinna; Zeri, Marcelo; Lasslop, Gitta et al

in Agricultural and Forest Meteorology (2010), 150(5), 684-691

Eddy covariance measurements were carried out at the Wetzstein site in Thuringia, Germany since December 2001. Soon after the start of the measurements night-time fluxes well above average CO2-fluxes ... [more ▼]

Eddy covariance measurements were carried out at the Wetzstein site in Thuringia, Germany since December 2001. Soon after the start of the measurements night-time fluxes well above average CO2-fluxes measured in temperate forest ecosystems were detected which could not be explained by biological processes but were valid with respect to standard quality criteria. The Wetzstein site is part of the CarboEurope-IP flux-network and the CO2-exchange of this spruce forest is of general ecological interest as the site is typical for central European spruce forest ecosystems at mountainous elevation. Additional investigations were made in order to identify the causes for the large difference between the flux balance and the inventory based NEP. Specific weather patterns and micrometeorological situations were identified during which a decoupling of the flows above and below the canopy leads to additional CO2-effluxes at the tower site which are not part of the net ecosystem exchange (NEE) at night. Rejecting data from these periods and gap-filling thereafter results in yearly sums of NEE, GPP and TER which are in better agreement with the biometric measurements at the tower site and comparable to other spruce forest sites. In this process ecosystem respiration was determined not only from extrapolation of nighttime data but also from flux partitioning based on day-time data using the hyperbolic light response function. It can be shown that flux measurements at this complex site need to be treated in a modified procedure compared to what is generally performed, namely extrapolating ecosystem respiration from night-time data. Using multiple data sources and applying a careful filtering of the data, confidence in the estimates of the carbon balance components increased. [less ▲]

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See detailAvailable energy and energy balance closure at four coniferous forest sites across Europe
Moderow, Uta; Aubinet, Marc ULg; Feigenwinter, Christian et al

in Theoretical & Applied Climatology (2009), 98(3-4), 397-412

The available energy (AE), driving the turbulent fluxes of sensible heat and latent heat at the earth surface, was estimated at four partly complex coniferous forest sites across Europe (Tharandt, Germany ... [more ▼]

The available energy (AE), driving the turbulent fluxes of sensible heat and latent heat at the earth surface, was estimated at four partly complex coniferous forest sites across Europe (Tharandt, Germany; Ritten/Renon, Italy; Wetzstein, Germany; Norunda, Sweden). Existing data of net radiation were used as well as storage change rates calculated from temperature and humidity measurements to finally calculate the AE of all forest sites with uncertainty bounds. Data of the advection experiments MORE II (Tharandt) and ADVEX (Renon, Wetzstein, Norunda) served as the main basis. On-site data for referencing and cross-checking of the available energy were limited. Applied cross checks for net radiation (modelling, referencing to nearby stations and ratio of net radiation to global radiation) did not reveal relevant uncertainties. Heat storage of sensible heat J (H), latent heat J (E), heat storage of biomass J (veg) and heat storage due to photosynthesis J (C) were of minor importance during day but of some importance during night, where J (veg) turned out to be the most important one. Comparisons of calculated storage terms (J (E), J (H)) at different towers of one site showed good agreement indicating that storage change calculated at a single point is representative for the whole canopy at sites with moderate heterogeneity. The uncertainty in AE was assessed on the basis of literature values and the results of the applied cross checks for net radiation. The absolute mean uncertainty of AE was estimated to be between 41 and 52 W m(-2) (10-11 W m(-2) for the sum of the storage terms J and soil heat flux G) during mid-day (approximately 12% of AE). At night, the absolute mean uncertainty of AE varied from 20 to about 30 W m(-2) (approximately 6 W m(-2) for J plus G) resulting in large relative uncertainties as AE itself is small. An inspection of the energy balance showed an improvement of closure when storage terms were included and that the imbalance cannot be attributed to the uncertainties in AE alone. [less ▲]

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See detailComparison of horizontal and vertical advective CO2 fluxes at three forest sites
Feigenwinter, Christian; Bernhofer, Christian; Eichelmann, Uwe et al

in Agricultural and Forest Meteorology (2008), 148(1), 12-24

Extensive field measurements have been performed at three CarboEurope-Integrated Project forest sites with different topography (Renon/Ritten, Italian Alps, Italy; Wetzstein, Thuringia, Germany; Norunda ... [more ▼]

Extensive field measurements have been performed at three CarboEurope-Integrated Project forest sites with different topography (Renon/Ritten, Italian Alps, Italy; Wetzstein, Thuringia, Germany; Norunda, Uppland, Sweden) to evaluate the relevant terms of the carbon balance by measuring CO2 concentrations [CO2] and the wind field in a 3D multi-tower cube setup. The same experimental setup (geometry and instrumentation) and the same methodology were applied to all the three experiments. It is shown that all sites are affected by advection in different ways and strengths. Everywhere, vertical advection (F-VA) occurred only at night. During the day, F-VA disappeared because of turbulent mixing, leading to a uniform vertical profile of [CO2]. Mean F-VA was nearly zero at the hilly site (wetzstein) and at the flat site (Norunda). However, large, momentary positive or negative contributions occurred at the flat site, whereas vertical non-turbulent fluxes were generally very small at the hilly site. At the slope site (Renon), F-VA was always positive at night because of the permanently negative mean vertical wind component resulting from downslope winds. Horizontal advection also occurred mainly at night. It was positive at the slope site and negative at the flat site in the mean diurnal course. The size of the averaged non-turbulent advective fluxes was of the same order of magnitude as the turbulent flux measured by eddy-covariance technique, but the scatter was very high. This implies that it is not advisable to use directly measured quantities of the non-turbulent advective fluxes for the estimation of net ecosystem exchange (NEE) on e.g. an hourly basis. However, situations with and without advection were closely related to local or synoptic meteorological conditions. Thus, it is possible to separate advection affected NEE estimates from fluxes which are representative of the source term. However, the development of a robust correction scheme for advection requires a more detailed site-specific analysis of single events for the identification of the relevant processes. This paper presents mean characteristics of the advective CO2 fluxes in a first site-to-site comparison and evaluates the main problems for future research. (c) 2007 Elsevier B.V. All rights reserved. [less ▲]

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