Kljun N.,University of Swansea |
Calanca P.,Institute for Sustainability science |
Rotach M.W.,University of Innsbruck |
Schmid H.P.,Institute of Meteorology and Climate Research
Geoscientific Model Development | Year: 2015
Flux footprint models are often used for interpretation of flux tower measurements, to estimate position and size of surface source areas, and the relative contribution of passive scalar sources to measured fluxes. Accurate knowledge of footprints is of crucial importance for any upscaling exercises from single site flux measurements to local or regional scale. Hence, footprint models are ultimately also of considerable importance for improved greenhouse gas budgeting. With increasing numbers of flux towers within large monitoring networks such as FluxNet, ICOS (Integrated Carbon Observation System), NEON (National Ecological Observatory Network), or AmeriFlux, and with increasing temporal range of observations from such towers (of the order of decades) and availability of airborne flux measurements, there has been an increasing demand for reliable footprint estimation. Even though several sophisticated footprint models have been developed in recent years, most are still not suitable for application to long time series, due to their high computational demands. Existing fast footprint models, on the other hand, are based on surface layer theory and hence are of restricted validity for real-case applications. To remedy such shortcomings, we present the two-dimensional parameterisation for Flux Footprint Prediction (FFP), based on a novel scaling approach for the crosswind distribution of the flux footprint and on an improved version of the footprint parameterisation of Kljun et al. (2004b). Compared to the latter, FFP now provides not only the extent but also the width and shape of footprint estimates, and explicit consideration of the effects of the surface roughness length. The footprint parameterisation has been developed and evaluated using simulations of the backward Lagrangian stochastic particle dispersion model LPDM-B (Kljun et al., 2002). Like LPDM-B, the parameterisation is valid for a broad range of boundary layer conditions and measurement heights over the entire planetary boundary layer. Thus, it can provide footprint estimates for a wide range of real-case applications. The new footprint parameterisation requires input that can be easily determined from, for example, flux tower measurements or airborne flux data. FFP can be applied to data of long-term monitoring programmes as well as be used for quick footprint estimates in the field, or for designing new sites. © 2015 Author(s).
Reisch C.,University of Regensburg |
Kaiser A.J.,Institute of Meteorology and Climate Research |
Horn A.,Stellenbosch University |
Poschlod P.,University of Regensburg
Plant Biology | Year: 2010
We investigated the influence of differing life history traits on the genetic structure of the related species Mimetes fimbriifolius and Mimetes hirtus (Proteaceae), which occur in the South African fynbos. Both species are bird-pollinated and ant-dispersed, but differ in rarity, longevity, ecological strategy and the fragmentation of their distribution area. We used AFLPs to study genetic variation within and between 21 populations of these two species across their distribution range. AFLP analysis revealed significantly higher genetic variation within populations of M. fimbriifolius than within M. hirtus. While M. fimbriifolius clearly lacked any significant genetic differentiation between populations, a distinct geographic pattern was observed for M. hirtus. Differentiation was, however, stronger at the regional (ΦΦPT = 0.57) than at the local scale (Φ ΦPT = 0.08). Our results clearly indicate that even closely related species that share the same mode of pollination and seed dispersal can differ in their genetic structure, depending on the magnitude of fragmentation, longevity of individuals and ecological strategy. © 2009 German Botanical Society and The Royal Botanical Society of the Netherlands.
Feng L.,University of Edinburgh |
Palmer P.I.,University of Edinburgh |
Parker R.J.,University of Leicester |
Deutscher N.M.,University of Bremen |
And 5 more authors.
Atmospheric Chemistry and Physics | Year: 2016
Estimates of the natural CO2 flux over Europe inferred from in situ measurements of atmospheric CO2 mole fraction have been used previously to check top-down flux estimates inferred from space-borne dry-air CO2 column (XCO2) retrievals. Several recent studies have shown that CO2 fluxes inferred from XCO2 data from the Japanese Greenhouse gases Observing SATellite (GOSAT) and the Scanning Imaging Absorption Spectrometer for Atmospheric CHartographY (SCIAMACHY) have larger seasonal amplitudes and a more negative annual net CO2 balance than those inferred from the in situ data. The cause of this elevated European uptake of CO2 is still unclear, but some recent studies have suggested that this is a genuine scientific phenomenon. Here, we put forward an alternative hypothesis and show that realistic levels of bias in GOSAT data can result in an erroneous estimate of elevated uptake over Europe. We use a global flux inversion system to examine the relationship between measurement biases and estimates of CO2 uptake from Europe. We establish a reference in situ inversion that uses an Ensemble Kalman Filter (EnKF) to assimilate conventional surface mole fraction observations and XCO2 retrievals from the surface-based Total Carbon Column Observing Network (TCCON). We use the same EnKF system to assimilate two independent versions of GOSAT XCO2 data. We find that the GOSAT-inferred European terrestrial biosphere uptake peaks during the summer, similar to the reference inversion, but the net annual flux is 1.40 ± 0.19 GtC a-1 compared to a value of 0.58 ± 0.14 GtC a-1 for our control inversion that uses only in situ data. To reconcile these two estimates, we perform a series of numerical experiments that assimilate observations with added biases or assimilate synthetic observations for which part or all of the GOSAT XCO2 data are replaced with model data. We find that for our global flux inversions, a large portion (60-90 %) of the elevated European uptake inferred from GOSAT data in 2010 is due to retrievals outside the immediate European region, while the remainder can largely be explained by a sub-ppm retrieval bias over Europe. We use a data assimilation approach to estimate monthly GOSAT XCO2 biases from the joint assimilation of in situ observations and GOSAT XCO2 retrievals. The inferred biases represent an estimate of systematic differences between GOSAT XCO2 retrievals and the inversion system at regional or sub-regional scales. We find that a monthly varying bias of up to 0.5 ppm can explain an overestimate of the annual sink of up to 0.20 GtC a-1. Our results highlight the sensitivity of CO2 flux estimates to regional observation biases, which have not been fully characterized by the current observation network. Without further dedicated measurements we cannot prove or disprove that European ecosystems are taking up a larger-than-expected amount of CO2. More robust inversion systems are also needed to infer consistent fluxes from multiple observation types. © 2016 Author(s).
Harrison S.P.,Macquarie University |
Morfopoulos C.,Imperial College London |
Dani K.G.S.,Macquarie University |
Prentice I.C.,Macquarie University |
And 12 more authors.
New Phytologist | Year: 2013
Approximately 1-2% of net primary production by land plants is re-emitted to the atmosphere as isoprene and monoterpenes. These emissions play major roles in atmospheric chemistry and air pollution-climate interactions. Phenomenological models have been developed to predict their emission rates, but limited understanding of the function and regulation of these emissions has led to large uncertainties in model projections of air quality and greenhouse gas concentrations. We synthesize recent advances in diverse fields, from cell physiology to atmospheric remote sensing, and use this information to propose a simple conceptual model of volatile isoprenoid emission based on regulation of metabolism in the chloroplast. This may provide a robust foundation for scaling up emissions from the cellular to the global scale. © 2012 New Phytologist Trust.
Bergmann J.,Helmholtz Center for Environmental Research |
Bergmann J.,University of Leipzig |
Bergmann J.,Institute of Meteorology and Climate Research |
Pompe S.,Helmholtz Center for Environmental Research |
And 4 more authors.
Plant Ecology | Year: 2010
The application of niche-based modelling techniques to plant species has not been explored for the majority of taxa in Europe, primarily due to the lack of adequate distributional data. However, it is of crucial importance for conservation adaptation decisions to assess and quantify the likely pool of species capable of colonising a particular region under altered future climate conditions. We here present a novel method that combines the species pool concept and information about shifts in analogous multidimensional climate space. This allows us to identify regions in Europe with a current climate which is similar to that projected for future time periods in Germany. We compared the extent and spatial location of climatically analogous European regions for three projected greenhouse gas emission scenarios in Germany for the time period 2071-2080 (+2. 4°C, +3. 3°C, +4. 5°C average increase in mean annual temperature) to those of the recent past in Europe (1961-90). Across all three scenarios, European land areas which are characterised by climatic conditions analogue to those found in Germany decreased from 14% in 1961-1990 to ca. 10% in 2071-2080. All scenarios show disappearing current climate types in Germany, which can mainly be explained with a general northwards shift of climatically analogous regions. We estimated the size of the potential species pool of these analogous regions using floristic inventory data for the Iberian Peninsula as 2,354 plant species. The identified species pool in Germany indicates a change towards warmth and drought adapted southern species. About one-third of the species from the Iberian analogous regions are currently already present in Germany. Depending on the scenario used, 1,372 (+2. 4°C average change of mean annual temperature), 1,399 (+3. 3°C) and 1,444 (+4. 5°C) species currently not found in Germany, occur in Iberian regions which are climatically analogous to German 2071-80 climate types. We believe that our study presents a useful approach to illustrate and quantify the potential size and spatial distribution of a pool of species potentially colonising new areas under changing climatic conditions. © Springer Science+Business Media B.V. 2009.
News Article | December 9, 2016
About 90 percent of precipitation over land depends on the formation of ice crystals in clouds, which fall down due to their increasing weight. But water in clouds only freezes when certain particles are present, on which ice crystals can grow. Of all aerosol particles, i.e. solid suspended particles in the atmosphere, however, only few act as ice nuclei. These rare aerosol particles decisively determine precipitation on earth. Hence, it is important to understand what makes them differ from other particles. "Such an understanding would improve our ability to predict ice and precipitation formation in a future changed climate with changed aerosol loading," says Professor Thomas Leisner, Head of the Atmospheric Aerosol Research Division of KIT's Institute of Meteorology and Climate Research (IMK-AAF). Scientists of IMK-AAF, in cooperation with researchers of the KIT Laboratory of Electron Microscopy (LEM) and University College London (UCL) have now succeeded in solving this question for the most important class of inorganic atmospheric ice nuclei, i.e. mineral dust particles consisting of feldspar. As is reported in the Science magazine, the scientists combined electron microscopy observations with molecular modeling to determine for the first time the atomic nature of this important inorganic ice nucleus. They showed that ice starts to grow on feldspar crystallites not on the accessible crystalline faces, but at microscopic defects like edges, cracks, and small depressions. Even though these defects are distributed randomly at the crystallite surface, the ice crystals grow with the same orientation relative to the feldspar crystal lattice. From these observations and from extensive molecular modeling, the scientists concluded that a specific crystal face that only occurs at defects on the surface of the feldspar crystallite is the underlying nucleus for ice formation. "Feldspar is one of the most active atmospheric ice nucleating agents, but why it is so good at making ice has remained unclear," said Professor Angelos Michaelides of UCL. "By identifying the active site for ice nucleation on feldspar, we have found an important piece of the puzzle." The researchers now expect similar studies to reveal the properties of other minerals acting as ice nuclei. Alexei Kiselev, Felix Bachmann, Philipp Pedevilla, Stephen J. Cox, Angelos Michaelides, Dagmar Gerthsen, and Thomas Leisner: Active sites in heterogeneous ice nucleation - the example of K-rich feldspars. Science, 2016. DOI: 10.1126/science.aai8034 More about the KIT Climate and Environment Center: http://www. . Karlsruhe Institute of Technology (KIT) pools its three core tasks of research, higher education, and innovation in a mission. With about 9,300 employees and 25,000 students, KIT is one of the big institutions of research and higher education in natural sciences and engineering in Europe. KIT - The Research University in the Helmholtz Association
Holst J.,Albert Ludwigs University of Freiburg |
Grote R.,Institute of Meteorology and Climate Research |
Offermann C.,Albert Ludwigs University of Freiburg |
Ferrio J.P.,Albert Ludwigs University of Freiburg |
And 3 more authors.
International Journal of Biometeorology | Year: 2010
We investigated the water balances of two beech stands (Fagus sylvatica L.) on opposite slopes (NE, SW) of a narrow valley near Tuttlingen in the southern Swabian Jura, a low mountain range in Southwest Germany. Our analysis combines results from continuous measurements of forest meteorological variables significant to the forest water balance, stand transpiration (ST) estimates from sap flow measurements, and model simulations of microclimate and water fluxes. Two different forest hydrological models (DNDC and BROOK90) were tested for their suitability to represent the particular sites. The investigation covers the years 2001-2007. Central aims were (1) to evaluate meteorological simulations of variables below the forest canopy, (2) to evaluate ST, (3) to quantify annual water fluxes for both beech stands using the evaluated hydrological models, and (4) to analyse the model simulations with regard to assumptions inherent in the respective model. Overall, both models were very well able to reproduce the observed dynamics of the soil water content in the uppermost 30 cm. However, the degree of fit depended on the year and season. The comparison of experimentally determined ST within the beech stand on the NE-slope during the growing season of 2007 with simulated transpiration did not yield a reliable statistical relationship. The simulation of water fluxes for the beech stand on the NE- and SW-slopes showed similar results for vegetation-related fluxes with both models, but different with respect to runoff and percolation flows. Overall, the higher evaporation demand on the warmer SW-slope did not lead to a significantly increased drought stress for the vegetation but was reflected mainly in decreased water loss from the system. This finding is discussed with regard to potential climate change and its impact on beech growth. © ISB 2009.
News Article | December 9, 2016
Ice crystals on a feldspar crystallite under the electron microscope. Although they grow on various levels of the feldspar, they have the same orientation. Credit: Alexei Kiselev and Dagmar Gerthsen, KIT In the atmosphere, feldspar particles act as ice nuclei that make ice crystals grow in clouds and enable precipitation. The discovery was made by researchers of Karlsruhe Institute of Technology (KIT) and University College London (UCL) with the help of electron microscopy observations and molecular dynamics computer modeling. The ice nucleus proper is a quasi-hidden crystal surface of the feldspar that is exposed at surface defects only. The researchers present their findings in Science. About 90 percent of precipitation over land depends on the formation of ice crystals in clouds, which fall down due to their increasing weight. But water in clouds only freezes when certain particles are present, on which ice crystals can grow. Of all aerosol particles, i.e. solid suspended particles in the atmosphere, however, only few act as ice nuclei. These rare aerosol particles decisively determine precipitation on earth. Hence, it is important to understand what makes them differ from other particles. "Such an understanding would improve our ability to predict ice and precipitation formation in a future changed climate with changed aerosol loading," says Professor Thomas Leisner, Head of the Atmospheric Aerosol Research Division of KIT's Institute of Meteorology and Climate Research (IMK-AAF). Scientists of IMK-AAF, in cooperation with researchers of the KIT Laboratory of Electron Microscopy (LEM) and University College London (UCL) have now succeeded in solving this question for the most important class of inorganic atmospheric ice nuclei, i.e. mineral dust particles consisting of feldspar. As is reported in Science, the scientists combined electron microscopy observations with molecular modeling to determine for the first time the atomic nature of this important inorganic ice nucleus. They showed that ice starts to grow on feldspar crystallites not on the accessible crystalline faces, but at microscopic defects like edges, cracks, and small depressions. Even though these defects are distributed randomly at the crystallite surface, the ice crystals grow with the same orientation relative to the feldspar crystal lattice. From these observations and from extensive molecular modeling, the scientists concluded that a specific crystal face that only occurs at defects on the surface of the feldspar crystallite is the underlying nucleus for ice formation. "Feldspar is one of the most active atmospheric ice nucleating agents, but why it is so good at making ice has remained unclear," said Professor Angelos Michaelides of UCL. "By identifying the active site for ice nucleation on feldspar, we have found an important piece of the puzzle." The researchers now expect similar studies to reveal the properties of other minerals acting as ice nuclei. More information: A. Kiselev et al. Active sites in heterogeneous ice nucleation—the example of K-rich feldspars, Science (2016). DOI: 10.1126/science.aai8034
Wagner S.,Institute of Meteorology and Climate Research |
Fersch B.,Institute of Meteorology and Climate Research |
Yuan F.,State Key Laboratory of Hydrology Water Resources and Hydraulic EngineeringHohai UniversityNanjing China |
Yu Z.,State Key Laboratory of Hydrology Water Resources and Hydraulic EngineeringHohai UniversityNanjing China |
Kunstmann H.,Institute of Meteorology and Climate Research
Water Resources Research | Year: 2016
A closed description of the regional water balance requires hydro-meteorological modeling systems which represent the atmosphere, land surface, and subsurface. We developed such a mesoscale modeling system, extending the atmospheric model WRF with the distributed hydrological model HMS in a fully coupled way. It includes explicit lateral groundwater and land surface flow parameterization schemes and two-way groundwater-unsaturated zone interaction by replacing the free drainage bottom boundary of WRF's Noah-LSM with a Fixed-head or Darcy-flux boundary condition. The system is exemplarily applied for the Poyang Lake basin (160,000 km2) and the period 1979-1986 using a two-nest approach covering East Asia (30 km) and the Poyang Lake basin (10 km) driven by ERA Interim. Stand-alone WRF effectively simulates temperature (bias 0.5°C) and precipitation (bias 21-26%). Stand-alone HMS simulations provide reasonable streamflow estimates. A significant impact on the regional water balance was found if groundwater-unsaturated zone interaction is considered. But the differences between the two groundwater coupling approaches are minor. For the fully coupled model system, streamflow results strongly depend on the simulation quality for precipitation. Two-way interaction results in net upward water fluxes in up to 25% of the basin area after the rainy season. In total, two-way interaction increases basin averaged recharge amounts. The evaluation with CPC and GLEAM indicates a better performance of the fully coupled simulation. The impact of groundwater coupling on LSM and atmospheric variables differs. Largest differences occur for the variable recharge (26%), whereas for atmospheric variables, the basin-averaged impact is minor (<1%). But locally, a spatial redistribution up to ±5% occurs for precipitation. © 2016. The Authors.
Dyroff C.,Institute of Meteorology and Climate Research |
Futterer D.,Institute of Meteorology and Climate Research |
Zahn A.,Institute of Meteorology and Climate Research
Applied Physics B: Lasers and Optics | Year: 2010
The tunable diode-laser absorption spectrometer ISOWAT for airborne measurements of the water-isotope ratios 18O/16O and D/H is described. The spectrometer uses a distributed feedback (DFB) diode laser to probe fundamental rovibrational water-absorption lines at around 2.66 μm. Very-low-noise system components along with signal averaging allow for a detection limit of 1.2 and 4.5‰ for measurements of 18O/ 16O and D/H, respectively, for a water-vapour mixing ratio of 100 ppmv and an averaging time of 60 s. This corresponds to a minimum detectable absorbance of ∼5×10-6 or ∼6.6×10-10 cm-1 when normalized to pathlength. In addition to its high sensitivity, the spectrometer is highly compact (19-inch rack at a height of 35 cm, excluding pump and calibration unit) and light weight (<40 kg total). The total power consumption is around 350 W, and the instrument is fully automated. ISOWAT will be calibrated during flight with known water-isotope ratios using a compact calibration-gas source. © 2009 Springer-Verlag.