Garmisch-Partenkirchen, Germany
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Yao Z.,CAS Institute of Atmospheric Physics | Yao Z.,Institute for Meteorology and Climate Research | Wu X.,Beijing Normal University | Wolf B.,Institute for Meteorology and Climate Research | And 5 more authors.
Journal of Geophysical Research: Atmospheres | Year: 2010

Changes in precipitation and temperature in Asian continental steppelands may affect soil physical, chemical and biological processes that control the biosphere-atmosphere exchange of N-trace gases. The changes include regional desertification, global warming and strong El Nio events that impact the large steppe land area in China and Mongolia. The area is so large that feedbacks to the global greenhouse gas balance may occur. In this study we investigated how changes in soil moisture and temperature, and especially drying-rewetting and freeze-thaw events, affect nitric oxide (NO) and nitrous oxide (N2O) fluxes from large intact soil cores taken from representative land use/cover types in the region of the Xilin River catchment, Inner Mongolia. These soil cores were incubated under varying conditions with respect to temperature (ranging from -10 to 15°C) and simulated rainfall (25, 45 and 65 mm). Following drying-rewetting and freeze-thaw transitions, we observed pulses of NO and N2O emissions from the soils of typical steppe, mountain meadow, sand dune and marshland. A comparable trend in soil CO2 emissions and soil air N2O concentrations indicated that the high substrate availability and rapid recovery of microbial activity after soil wetting and thawing resulted in high gas fluxes. Across the whole temperature range, NO and N2O fluxes from all soils, except for N2O emissions from marshland soils, showed a positive exponential relationship with soil temperature. A combination of soil temperature and soil moisture explained most of the observed variations in NO (up to 74-90%) and N2O (up to 67-89%) fluxes for individual soils. Spatial differences in NO emissions between land use/cover types could be explained by differences in soil organic carbon and pH, whereas spatial variations of N2O fluxes were primarily correlated with differences in soil microbial biomass. On the basis of the incubation under controlled conditions, the average annual flux, weighted by the areal extent of the different investigated land use/cover types in the region, was estimated at ∼3.9 ± 1.1 kg N ha-1 yr-1 for NO and 0.53 ± 0.20 kg N ha-1 yr-1 for N 2O, respectively. It is noteworthy that our measurements were conducted using soil cores without a vegetation cover, which probably resulted in an overestimation of N-trace gas fluxes. However, our results indicate that the rarely determined NO formation appears to be a significant pathway in the N cycle of semiarid steppe, which is highly sensitive to the climatic change taking place in these regions, especially an increase in intensity and frequency of drying-wetting and freeze-thaw cycles. © 2010 by the American Geophysical Union.

Werner C.,Biodiversity and Climate Research Center | Werner C.,Institute for Meteorology and Climate Research | Reiser K.,Institute for Meteorology and Climate Research | Dannenmann M.,Institute for Meteorology and Climate Research | And 3 more authors.
Biogeosciences | Year: 2014

Strong seasonal variability of hygric and thermal soil conditions are a defining environmental feature in northern Australia. However, how such changes affect the soil-atmosphere exchange of nitrous oxide (N2O), nitric oxide (NO) and dinitrogen (N2) is still not well explored. By incubating intact soil cores from four sites (three savanna, one pasture) under controlled soil temperatures (ST) and soil moisture (SM) we investigated the release of the trace gas fluxes of N2O, NO and carbon dioxide (CO2). Furthermore, the release of N2 due to denitrification was measured using the helium gas flow soil core technique. Under dry pre-incubation conditions NO and N2O emissions were very low (< 7:0 ± 5:0 μg NO-N m-2 h-1; < 0:0 ± 1:4 μg N2O-N m-2 h-1) or in the case of N2O, even a net soil uptake was observed. Substantial NO (max: 306.5 μg N m-2 h-1) and relatively small N2O pulse emissions (max: 5:8 ± 5:0 μg N m-2 h-1) were recorded following soil wetting, but these pulses were short lived, lasting only up to 3 days. The total atmospheric loss of nitrogen was generally dominated by N2 emissions (82.4-99.3% of total N lost), although NO emissions contributed almost 43.2% to the total atmospheric nitrogen loss at 50% SM and 30°C ST incubation settings (the contribution of N2 at these soil conditions was only 53.2 %). N2O emissions were systematically higher for 3 of 12 sample locations, which indicates substantial spatial variability at site level, but on average soils acted as weak N2O sources or even sinks. By using a conservative upscale approach we estimate total annual emissions from savanna soils to average 0.12 kg N ha-1 yr-1 (N2O), 0.68 kg N ha-1 yr-1 (NO) and 6.65 kg N ha-1 yr-1 (N2). The analysis of long-term SM and ST records makes it clear that extreme soil saturation that can lead to high N2O and N2 emissions only occurs a few days per year and thus has little impact on the annual total. The potential contribution of nitrogen released due to pulse events compared to the total annual emissions was found to be of importance for NO emissions (contribution to total: 5-22 %), but not for N2O emissions. Our results indicate that the total gaseous release of nitrogen from these soils is low and clearly dominated by loss in the form of inert nitrogen. Effects of seasonally varying soil temperature and moisture were detected, but were found to be low due to the small amounts of available nitrogen in the soils (total nitrogen < 0:1 %). © Author(s) 2014.

News Article | December 5, 2016

Population is growing, climate is warming - hence, emission of ammonia (NH3) trace gas from e.g. agriculture will increase worldwide. Recently, scientists of Karlsruhe Institute of Technology (KIT) for the first time detected NH3 in the upper troposphere. Together with researchers from Colorado/USA and Mexico, they analyzed satellite measurements by the MIPAS infrared spectrometer and found increased amounts of NH3 between 12 and 15 km height in the area of the Asian monsoon. This suggests that the gas is responsible for the formation of aerosols, smallest particles that might contribute to cloud formation. The researchers present their work in the Atmospheric Chemistry and Physics journal. (DOI: 10.5194/acp-16-14357-2016) Ammonia, a chemical compound of nitrogen and hydrogen, mainly originates from agricultural processes, in particular from lifestock farming and fertilization. Wide application of ammonia as a basic substance of fertilizers became possible by the development of artificial ammonia synthesis in Karlsruhe more than 100 years ago. Today, highest ammonia emissions are encountered in North India and Southeast China. Due to population growth and global warming, global ammonia emissions are expected to increase strongly in the future. Gaseous ammonia reacts with acids, such as sulfuric acid or nitric acid, to the corresponding ammonium salts. However, ammonia does not only pollute the ecosystems. Particles of ammonium salts can attach to each other and form aerosol particles acting as condensation nuclei in cloud formation. Such aerosols of anthropogenic origin have a cooling effect in the atmosphere and might compensate part of the anthropogenic greenhouse effect. In this connection, it is important to determine vertical distribution of atmospheric ammonia. Concentrations of ammonia in the middle and upper troposphere, the bottom layer of the atmosphere, have hardly been studied so far. Now, researchers of the Atmospheric Trace Gases and Remote Sensing Division of KIT's Institute for Meteorology and Climate Research (IMK-ASF) as well as of the University of Colorado at Boulder and the Universidad Nacional Autónoma de México for the first time detected ammonia in the upper troposphere. They evaluated measurements made by the MIPAS infrared spectrometer on the European environmental satellite ENVISAT from 2002 to 2012. MIPAS, an instrument designed by KIT, recorded highly resolved spectra in the middle infrared range, from which gases can be identified clearly. Every gas emits specific infrared radiation. The scientists calculated the average of three-month measurements in areas of ten degrees longitude and ten degrees latitude each. At 12 to 15 km height, in the area of the Asian monsoon, they found an increased concentration of ammonia of up to 33 pptv (33 NH3 molecules per trillion air molecules). Similarly high concentrations were measured in no other season and no other region. "Observations show that ammonia is not washed out completely when air ascends in monsoon circulation. Hence, it enters the upper troposphere from the boundary layer close to the ground, where the gas occurs at relatively high concentrations," Dr. Michael Höpfner, Head of the Remote Sensing Using Aircraft and Balloons Group of IMK-ASF. "It is therefore assumed that part of the Asian tropopause aerosol layer consists of ammonium salts." Outside of the area of the Asian monsoon, concentrations of ammonia in the upper troposphere were found to be below the detection limit of a few pptv. This finding can contribute to refining global models. As far as the Asian monsoon is concerned, a large measurement campaign with the GLORIA instrument is planned in 2017. GLORIA is a novel type of infrared camera that decomposes the thermal radiation emitted by atmospheric gases into its spectral colors and, hence, yields ammonia concentration results near the tropopause, the boundary layer between the troposphere and the above stratosphere, of higher temporal and spatial - horizontal and vertical - resolution. Michael Höpfner, Rainer Volkamer, Udo Grabowski, Michel Grutter, Johannes Orphal, Gabriele Stiller, Thomas von Clarmann, and Gerald Wetzel: First detection of ammonia (NH3) in the Asian summer monsoon upper troposphere. Atmospheric Chemistry and Physics, 2016. DOI: 10.5194/acp-16-14357-2016 For further information, please contact: Margarete Lehné, Press Officer, Phone: +49 721 608-4 8121, Fax: +49 721 608-4 3658, Email: 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 Since 2010, the KIT has been certified as a family-friendly university. This press release is available on the internet at http://www. .

Baumgaertner A.J.G.,Max Planck Institute for Chemistry | Jockel P.,Max Planck Institute for Chemistry | Jockel P.,German Aerospace Center | Riede H.,Max Planck Institute for Chemistry | And 2 more authors.
Atmospheric Chemistry and Physics | Year: 2010

The atmospheric chemistry general circulation model ECHAM5/MESSy (EMAC) has been extended by processes that parameterize particle precipitation. Several types of particle precipitation that directly affect NOy and HOx concentrations in the middle atmosphere are accounted for and discussed in a series of papers. In part 1, the EMAC parameterization for NOx produced in the upper atmosphere by low-energy electrons is presented. Here, we discuss production of NOy and HOx associated with Solar Proton Events (SPEs). A submodel that parameterizes the effects of precipitating protons, based on flux measurements by instruments on the IMP or GOES satellites, was added to the EMAC model. Production and transport of NOy and HOx, as well as effects on other chemical species and dynamics during the 2003 Halloween SPEs are presented. Comparisons with MIPAS/ENVISAT measurements of a number of species affected by the SPE are shown and discussed. There is good agreement for NO2, but a severe disagreement is found for N2O similar to other studies. We discuss the effects of an altitude dependence of the N/NO production rate on the N2O and NOy changes during the SPE. This yields a modified parameterization that shows mostly good agreement between MIPAS and model results for NO2, N2O, O3, and HOC l. With the ability of EMAC to relax the model meteorology to observations, accurate assessment of total column ozone loss is also possible, yielding a loss of approximately 10 DU at the end of November. Discrepancies remain for HNO3, N2O5, and ClONO2, which are likely a consequence from the missing cluster ion chemistry and ion-ion recombination in the EMAC model as well as known issues with the model's NOy partitioning. © 2011 Author(s).

Wang C.,CAS Institute of Botany | Butterbach-Bahl K.,Institute for Meteorology and Climate Research | Han Y.,CAS Institute of Botany | Wang Q.,CAS Institute of Botany | And 3 more authors.
Plant and Soil | Year: 2011

There is an increasing demand for the sustainable management of old-field communities in northern China, which have developed on abandoned cropland on formerly converted natural steppe sites, to regain forage yield, biodiversity, and soil fertility. In thus study we examined how two management options-clipping and nitrogen (N) addition-may affect net >microbial N mineralization (ammonification + nitrification), microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and microbial respirations (MR) in grass dominated, herb dominated, and grass-herb mixed patches in an old-field community in northern China. Topsoil (0-10 cm) net N mineralization rate was 177% and 69% higher in mixed grass and herb patches (patch B) as compared to unmixed grass (patch A) or herb (patch C) patches, respectively. Topsoil MBN was significantly different among the three patches with the highest value for soils taken from umixed grass patches. However, patches with mixed grass and herb or herb dominated patches had 12% higher microbial respiration (MR) than unmixed grass patch. Clipping and N addition had no effects on net N mineralization or MBC, but both treatments decreased MBN and MR and increased the ratio between microbial biomass C and microbial biomass N (MBC/MBN) in the growing season. Incubation of soil cores under optimal water and temperature conditions in the laboratory showed that the response of microbial N transformations in soils under different vegetation patches to experimental N addition and clipping was limited by soil water availability. Our results strongly highlight the need to further study the importance of belowground C supply as a control of microbial N cycling processes. It also suggests that during the restoration process of degenerated croplands N cycling rates are stimulated, but that the magnitude of this stimulation is modulated by plant community composition of the old-fields. © 2010 Springer Science+Business Media B.V.

Berg P.,Institute for Meteorology and Climate Research | Haerter J.O.,Max Planck Institute for Meteorology
Atmospheric Research | Year: 2013

Using synoptic weather types and comparing high-resolution precipitation and temperature station data, a separation of large-scale and convective precipitation events is performed. We present percentiles of both types and their superposition for varying precipitation accumulation timescales. In some temperature ranges, large-scale, convective and total precipitation percentiles follow increases with temperature at rates higher than that of the saturation humidity increase of the atmosphere of roughly 7% per degree Kelvin - as given by the Clausius-Clapeyron (CC) relation. However, the increase in total precipitation is found to be due to the transition between the corresponding percentiles of the large-scale and convective types, rather than their individual sections of steep increase. Furthermore, convective precipitation displays a leveling-off towards higher temperatures. This poses further challenges to reconcile arguments brought forward elsewhere - namely those suggesting convective precipitation as the driver of the super-CC increase - with the present observational data. © 2011 Elsevier B.V.

Van Der Ent R.J.,Technical University of Delft | Tuinenburg O.A.,Wageningen University | Tuinenburg O.A.,University Pierre and Marie Curie | Knoche H.-R.,Institute for Meteorology and Climate Research | And 3 more authors.
Hydrology and Earth System Sciences | Year: 2013

This paper compares state-of-the-art atmospheric moisture tracking models. Such models are typically used to study the water component of coupled land and atmosphere models, in particular quantifying moisture recycling and the source-sink relations between evaporation and precipitation. There are several atmospheric moisture tracking methods in use. However, depending on the level of aggregation, the assumptions made and the level of detail, the performance of these methods may differ substantially. In this paper, we compare three methods. The RCM-tag method uses highly accurate 3-D water tracking (including phase transitions) directly within a regional climate model (online), while the other two methods (WAM and 3D-T) use a posteriori (offline) water vapour tracking. The original version of WAM is a single-layer model, while 3D-T is a multi-layer model, but both make use the "well-mixed" assumption for evaporation and precipitation. The a posteriori models are faster and more flexible, but less accurate than online moisture tracking with RCM-tag. In order to evaluate the accuracy of the a posteriori models, we tagged evaporated water from Lake Volta in West Africa and traced it to where it precipitates. It is found that the strong wind shear in West Africa is the main cause of errors in the a posteriori models. The number of vertical layers and the initial release height of tagged water in the model are found to have the most significant influences on the results. With this knowledge small improvements have been made to the a posteriori models. It appeared that expanding WAM to a 2-layer model, or a lower release height in 3D-T, led to significantly better results. Finally, we introduced a simple metric to assess wind shear globally and give recommendations about when to use which model. The "best" method, however, very much depends on the research question, the spatial extent under investigation, as well as the available computational power. © 2013 Author(s).

Nicolet M.,ETH Zurich | Stetzer O.,ETH Zurich | Luond F.,ETH Zurich | Mohler O.,Institute for Meteorology and Climate Research | Lohmann U.,ETH Zurich
Atmospheric Chemistry and Physics | Year: 2010

In order to determine the efficiency of different aerosol particles to nucleate ice, an Ice Optical DEpolarization detector (IODE) was developed to distinguish between water droplets and ice crystals in ice nucleation chambers. A laser beam polarized linearly (power: 50 mW, wavelength: 407 nm) is directed through the chamber. The scattered light intensity from particles is measured at a scattering angle of Θ=175° in both polarization components (parallel and perpendicular). The ratio between the perpendicular intensity over the total one yields the depolarization ratio δ. Single particle detection is possible, using a peak detection algorithm. For high particle concentrations, a real-time signal averaging method can also be run simultaneously. The IODE detector was used in connection with the Zurich ice nucleation chamber during the ICIS 2007 workshop where ice nucleation experiments were performed with several aerosol types. In presence of ice crystals, a depolarization ratio could be measured on a particle-by-particle basis. Mean values of δranged from 0.24 to 0.37 and agree well with theoretical calculations.

Berg P.,Institute for Meteorology and Climate Research | Feldmann H.,Institute for Meteorology and Climate Research | Panitz H.-J.,Institute for Meteorology and Climate Research
Journal of Hydrology | Year: 2012

Bias correction of varying complexity - from simple scaling and additive corrections to more advanced histogram equalisation (HE) corrections - is applied to high resolution (7. km) regional climate model (RCM) simulations. The aim of the study is to compare different methods that are easily implemented and applied to the data, and to assess the applicability and impact of the bias correction depending on the type of bias. The model bias is determined by comparison to a new gridded high resolution (1. km) data set of temperature and precipitation, which is also used as reference for the corrections. The performance of the different methods depends on the type of bias of the model, and on the investigated statistic. Whereas simpler methods correct the first moment of the distributions, they can have adverse effects on higher moments. The HE method corrects also higher moments, but approximations of the transfer function are necessary when applying the method to other data than the calibration data. Here, an empirical transfer function with linear fits to the tails is compared to a version where the complete function is approximated by a linear fit. The latter is thus limited to corrections of the first and second moments of the distribution. While making the transfer function more generally applicable, these approximations also limit the performance of the HE method. For the current model biases, the linear approximation is found suitable for precipitation, but for temperature it is not able to correct the whole distribution. The lower performance of the linear correction is most pronounced in summer, and is likely due to a difference in skewness between the model and observational data. Further limitations of the HE method are due to the need for long time series in order to have robust distributions for calculating the transfer function. Theoretical approximations of the required length of the calibration period were performed by using different sampling sizes drawn from a known distribution. The excerise show that about 30. year long time series are needed to have reasonable accuracy for the estimation of variance, when also corrections of the annual cycle is required. © 2012 Elsevier B.V..

Yao Z.,CAS Institute of Atmospheric Physics | Yao Z.,Institute for Meteorology and Climate Research | Zhou Z.,CAS Institute of Atmospheric Physics | Zheng X.,CAS Institute of Atmospheric Physics | And 5 more authors.
Plant and Soil | Year: 2010

Organic matter addition is thought to be an important regulator of nitrous oxide (N2O) emissions from croplands. Contradictory effects, however, were reported in previous studies. To investigate the effects of crop residue management on N2O emissions from rice-wheat rotation ecosystems, we conducted field experiments at three sites (Suzhou, Wuxi and Jiangdu) in the Yangtze River Delta, using static chamber and gas chromatography methods. Our data show that N2O emissions throughout the rice season from plots treated with wheat straw application at a high rate (WS) prior to rice transplanting (1. 1-2. 0 kg N ha-1) were significantly lower (P < 0. 05) than those from the control plots without organic matter addition or added with wheat straw at a moderate rate (1. 6-2. 9 kg N ha-1). Furthermore, the WS treatments had a residual inhibitory effect on N2O emissions in the following non-rice season, which consistently resulted in significantly lower emissions (P < 0. 05) compared to the control treatments (2. 2-3. 1 vs. 3. 9-5. 6 kg N ha-1). In comparison to the control treatments, the WS treatments reduced both the seasonal and annual direct emission factors of the applied nitrogen (EFd) by 50-68% (mean: 57%). The addition of compost (aerobically composted rice or wheat straw harvested in the last rotation) reduced the seasonal and annual EFds by 29-32%. Over the entire rice-wheat rotation cycle, annual N2O emissions from the fertilized fields at the three sites ranged from 3. 3 ± 0. 3 to 16. 8 ± 0. 6 kg N ha-1, with a coefficient of variation (CV) of 61%. Similarly, the EFds during the rice-wheat rotation cycle ranged from 0. 4% to 2. 5%, with a CV of 67%. These high spatial variations might have been related to: variations in soil properties, such as texture and soil organic carbon; management practices, such as straw treatments (i. e., compost versus fresh straw) and weather conditions, such as precipitation and rainfall distribution. Our results indicate that the incorporation of fresh wheat straw at a high rate during the rice season is an effective management practice for the mitigation of N2O emissions in rice-wheat rotation systems. Whether this practice is also effective in reducing the overall global warming potential of net N2O, CH4 and CO2 emissions needs to be seen through further studies. © Springer Science + Business Media B.V. 2009.

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