Bodo Wichura

Bio: Bodo Wichura is an academic researcher from Deutscher Wetterdienst. The author has contributed to research in topics: Carbon sink & Solar eclipse. The author has an hindex of 6, co-authored 13 publications receiving 1463 citations. Previous affiliations of Bodo Wichura include University of Bayreuth.

Micrometeorological measurements during the total solar eclipse of August 11, 1999

Abstract: Micrometeorological measurements of radiation, atmospheric and soil parameters, and turbulent energy and momentum e uxes, ozone and carbon dioxide e uxes have been conducted over a maize e eld at FreisingWeihenstephan in Southern Germany during the total solar eclipse on August 11, 1999. For the period 30 minutes before and after the totality the weather conditions at the location where the micrometeorological measurements were made was satisfactory. Several connections between the irradiation and other meteorological parameters over a maize e eld have been found. The time response between irradiation and the long-wave upward radiation was only a few minutes, whereas almost all parameters caused by the turbulent transport had a time shift of up to 30 minutes. A period of nearly 30 minutes with reduced turbulence regime after the totality was found. Using a wavelet transformation for the time series, a change of time scales from longer to shorter ones was observed before the totality, and after the turbulence increased in the short time scales. The investigation of the residuum of the closure of the energy balance showed that with a time shift for the latent heat e ux (unlike the net radiation) after the totality, a better energy budget closure was obtained.

Carbon budget of a spruce forest ecosystem

Abstract: The investigation of carbon fluxes is of immense interest in ecosystem and climate research. Forest ecosystems may be a sink for anthropogenic carbon, if the assimilation is larger than the respiration. Alternatively, increasing temperatures due to climate change (IPCC 2001) may be a reason for increasing respiratory fluxes. While low-altitude spruce sites in Germany are significant carbon sinks (e.g. Bernhofer et al. 2003), sites above 600 m a.s.l. are only small sinks or may change their character by climate change. Therefore the Weidenbrunnen site in the Lehstenbach catchment was selected as a EUROFLUX site (Valentini et al. 2000) and was also used in the following CARBOEUROFLUX program for systematic investigations with respect to the data quality of turbulent fluxes. Overviews of the European carbon program and of the worldwide FLUXNET program are respectively given by Valentini (2003) and Baldocchi et al. (2001). All relevant references are also provided herein. Furthermore, the site was used for process studies to separate assimilation and respiration fluxes, and to study the exchange conditions between the forest and the atmosphere (Wichura et al., this Vol.). All of these studies were part of the ecosystem research of the Lehstenbach catchment, the main research area of the Bayreuth Institute of Terrestrial Ecosystem Research (BITOK). The main results for the carbon dioxide flux measurements since 1997 are discussed in this chapter.

The BAYSOFI Campaign - Measurements Carried out during the Total Solar Eclipse of August 11, 1999

Abstract: The total solar eclipse of August 11, 1999 provided a unique opportunity to observe the input of fast day-night and night-day transitions, under high solar elevation around noon, on the earth-atmosphere-biosphere system. Within the interdisciplinary e eld campaign BAYSOFI, measurements of radiation, boundary layer micrometeorology and photochemistry, photosynthesis and transpiration were carried out at Freising-Weihenstephan and several locations nearby focusing on short-term effects of the eclipse. Although the overall grosswetterlage on August 11 was not favourable for viewing the eclipse, with clouds covering most of central Europe, observational conditions at Weihenstephan were fair due to a large hole in the cloud layer which appeared just half hour before totality lasting for more than one hour. Thus signie cant effects of the eclipse on radiation, photolysis rates, OH, the temperature, wind, turbulence structure and stratie cation, ozone and CO 2 e uxes, photosynthesis, transpiration and sap e ow of trees could be observed which are reported and discussed in the following sequence of papers.

Structure of carbon dioxide exchange processes above a spruce forest

Abstract: Several micrometeorological techniques,’such as the flux-gradient method or the eddy covariance technique, offer the potential to measure net fluxes of water vapor, CO2 and other trace gases exchanged between ecosystems and the atmosphere (e.g., Baldocchi and Meyers 1998). Subsequent data analyses allow the calculation of net ecosystem CO2 exchange. These net fluxes, however, reflect the balance between different component fluxes. In the case of CO2, two opposing fluxes contribute to this net flux: CO2 uptake during photosynthesis and CO2 release during respiration from above- and belowground organisms. Distinguishing among these components is critical to obtain insights into the processes underlying ecosystem responses to climate forcing (Buchmann 2002). This is because environmental parameters, such as temperature and soil moisture, differentially affect biological activities (e.g., Baldocchi et al. 2001).

FLUXNET: A New Tool to Study the Temporal and Spatial Variability of Ecosystem-Scale Carbon Dioxide, Water Vapor, and Energy Flux Densities

Abstract: FLUXNET is a global network of micrometeorological flux measurement sites that measure the exchanges of carbon dioxide, water vapor, and energy between the biosphere and atmosphere. At present over 140 sites are operating on a long-term and continuous basis. Vegetation under study includes temperate conifer and broadleaved (deciduous and evergreen) forests, tropical and boreal forests, crops, grasslands, chaparral, wetlands, and tundra. Sites exist on five continents and their latitudinal distribution ranges from 70°N to 30°S. FLUXNET has several primary functions. First, it provides infrastructure for compiling, archiving, and distributing carbon, water, and energy flux measurement, and meteorological, plant, and soil data to the science community. (Data and site information are available online at the FLUXNET Web site, http://www-eosdis.ornl.gov/FLUXNET/.) Second, the project supports calibration and flux intercomparison activities. This activity ensures that data from the regional networks are intercomparable. And third, FLUXNET supports the synthesis, discussion, and communication of ideas and data by supporting project scientists, workshops, and visiting scientists. The overarching goal is to provide information for validating computations of net primary productivity, evaporation, and energy absorption that are being generated by sensors mounted on the NASA Terra satellite. Data being compiled by FLUXNET are being used to quantify and compare magnitudes and dynamics of annual ecosystem carbon and water balances, to quantify the response of stand-scale carbon dioxide and water vapor flux densities to controlling biotic and abiotic factors, and to validate a hierarchy of soil–plant–atmosphere trace gas exchange models. Findings so far include 1) net CO 2 exchange of temperate broadleaved forests increases by about 5.7 g C m −2 day −1 for each additional day that the growing season is extended; 2) the sensitivity of net ecosystem CO 2 exchange to sunlight doubles if the sky is cloudy rather than clear; 3) the spectrum of CO 2 flux density exhibits peaks at timescales of days, weeks, and years, and a spectral gap exists at the month timescale; 4) the optimal temperature of net CO 2 exchange varies with mean summer temperature; and 5) stand age affects carbon dioxide and water vapor flux densities.

On the Separation of Net Ecosystem Exchange into Assimilation and Ecosystem Respiration: Review and Improved Algorithm

Abstract: This paper discusses the advantages and disadvantages of the different methods that separate net ecosystem exchange (NEE) into its major components, gross ecosystem carbon uptake (GEP) and ecosystem respiration (Reco). In particular, we analyse the effect of the extrapolation of night-time values of ecosystem respiration into the daytime; this is usually done with a temperature response function that is derived from long-term data sets. For this analysis, we used 16 one-year-long data sets of carbon dioxide exchange measurements from European and US-American eddy covariance networks. These sites span from the boreal to Mediterranean climates, and include deciduous and evergreen forest, scrubland and crop ecosystems. We show that the temperature sensitivity of Reco, derived from long-term (annual) data sets, does not reflect the short-term temperature sensitivity that is effective when extrapolating from night- to daytime. Specifically, in summer active ecosystems the long

Assessing the eddy covariance technique for evaluating carbon dioxide exchange rates of ecosystems: past, present and future

Abstract: The eddy covariance technique ascertains the exchange rate of CO2 across the interface between the atmosphere and a plant canopy by measuring the covariance between fluctuations in vertical wind velocity and CO2 mixing ratio. Two decades ago, the method was employed to study CO2 exchange of agricultural crops under ideal conditions during short field campaigns. During the past decade the eddy covariance method has emerged as an important tool for evaluating fluxes of carbon dioxide between terrestrial ecosystems and the atmosphere over the course of a year, and more. At present, the method is being applied in a nearly continuous mode to study carbon dioxide and water vapor exchange at over a hundred and eighty field sites, worldwide. The objective of this review is to assess the eddy covariance method as it is being applied by the global change community on increasingly longer time scales and over less than ideal surfaces. The eddy covariance method is most accurate when the atmospheric conditions (wind, temperature, humidity, CO2) are steady, the underlying vegetation is homogeneous and it is situated on flat terrain for an extended distance upwind. When the eddy covariance method is applied over natural and complex landscapes or during atmospheric conditions that vary with time, the quantification of CO2 exchange between the biosphere and atmosphere must include measurements of atmospheric storage, flux divergence and advection. Averaging CO2 flux measurements over long periods (days to year) reduces random sampling error to relatively small values. Unfortunately, data gaps are inevitable when constructing long data records. Data gaps are generally filled with values produced from statistical and empirical models to produce daily and annual sums of CO2 exchange. Filling data gaps with empirical estimates do not introduce significant bias errors because the empirical algorithms are derived from large statistical populations. On the other hand, flux measurement errors can be biased at night when winds are light and intermittent. Nighttime bias errors tend to produce an underestimate in the measurement of ecosystem respiration. Despite the sources of errors associated with long-term eddy flux measurements, many investigators are producing defensible estimates of annual carbon exchange. When measurements come from nearly ideal sites the error bound on the net annual exchange of CO2 is less than ±50 g C m−2 yr−1. Additional confidence in long-term measurements is growing because investigators are producing values of net ecosystem productivity that are converging with independent values produced by measuring changes in biomass and soil carbon, as long as the biomass inventory studies are conducted over multiple years.