bluuebunny/crossref_metadata_2025 huggingface dataset:
Why do general circulation models overestimate the aerosol cloud lifetime effect? A case study comparing CAM5 and a CRM
Authors: Zhou Cheng , Penner Joyce E.
Published: January 2017

Abstract. Observation-based studies have shown that the aerosol cloud lifetime effect or the increase of cloud liquid water path (LWP) with increased aerosol loading may have been overestimated in climate models. Here, we simulate shallow warm clouds on 27 May 2011 at the southern Great Plains (SGP) measurement site established by the Department of Energy's (DOE) Atmospheric Radiation Measurement (ARM) program using a single-column version of a global climate model (Community Atmosphere Model or CAM) and a cloud resolving model (CRM). The LWP simulated by CAM increases substantially with aerosol loading while that in the CRM does not. The increase of LWP in CAM is caused by a large decrease of the autoconversion rate when cloud droplet number increases. In the CRM, the autoconversion rate is also reduced, but this is offset or even outweighed by the increased evaporation of cloud droplets near the cloud top, resulting in an overall decrease in LWP. Our results suggest that climate models need to include the dependence of cloud top growth and the evaporation/condensation process on cloud droplet number concentrations.
Air quality improvement in a megacity: implications from 2015 Beijing Parade Blue pollution control actions
Authors: Xu Wen , Song Wei , Zhang Yangyang , Liu Xuejun , Zhang Lin , Zhao Yuanhong , Liu Duanyang , Tang Aohan , Yang Daowei , Wang Dandan , Wen Zhang , Pan Yuepeng , Fowler David , Collett Jr. Jeffrey L. , Erisman Jan Willem , Goulding Keith , Li Yi , Zhang Fusuo
Published: January 2017

Abstract. The implementation of strict emission control measures in Beijing and surrounding regions during the 2015 China Victory Day Parade provided a valuable opportunity to investigate related air quality improvements in a megacity. We measured NH3, NO2 and PM2.5 at multiple sites in and outside Beijing and summarized concentrations of PM2.5, PM10, NO2, SO2 and CO in 291 cities across China from a national urban air quality monitoring network between August and September 2015. Consistently significant reductions of 12–35 % for NH3 and 33–59 % for NO2 in different areas of Beijing during the emission control period (referred to as the Parade Blue period) were observed compared with measurements in the pre- and post-Parade Blue periods without emission controls. Average NH3 and NO2 concentrations at sites near traffic were strongly correlated and showed positive and significant responses to traffic reduction measures, suggesting that traffic is an important source of both NH3 and NOx in urban Beijing. Daily concentrations of PM2.5 and secondary inorganic aerosol (sulfate, ammonium and nitrate) at the urban and rural sites both decreased during the Parade Blue period. During (after) the emission control period, concentrations of PM2.5, PM10, NO2, SO2 and CO from the national city-monitoring network showed the largest decrease (increase) of 34–72 % (50–214 %) in Beijing, a smaller decrease (a moderate increase) of 1–32 % (16–44 %) in emission control regions outside Beijing and an increase (decrease) of 6–16 % (−2–7 %) in non-emission-control regions of China. Integrated analysis of modelling and monitoring results demonstrated that emission control measures made a major contribution to air quality improvement in Beijing compared with a minor contribution from favourable meteorological conditions during the Parade Blue period. These results show that controls of secondary aerosol precursors (NH3, SO2 and NOx) locally and regionally are key to curbing air pollution in Beijing and probably in other mega cities worldwide.
Atmospheric CO2 observations and models suggest strong carbon uptake by forests in New Zealand
Authors: Steinkamp Kay , Mikaloff Fletcher Sara E. , Brailsford Gordon , Smale Dan , Moore Stuart , Keller Elizabeth D. , Baisden W. Troy , Mukai Hitoshi , Stephens Britton B.
Published: January 2017

Abstract. A regional atmospheric inversion method has been developed to determine the spatial and temporal distribution of CO2 sinks and sources across New Zealand for 2011–2013. This approach infers net air–sea and air–land CO2 fluxes from measurement records, using back-trajectory simulations from the Numerical Atmospheric dispersion Modelling Environment (NAME) Lagrangian dispersion model, driven by meteorology from the New Zealand Limited Area Model (NZLAM) weather prediction model. The inversion uses in situ measurements from two fixed sites, Baring Head on the southern tip of New Zealand's North Island (41.408° S, 174.871° E) and Lauder from the central South Island (45.038° S, 169.684° E), and ship board data from monthly cruises between Japan, New Zealand, and Australia. A range of scenarios is used to assess the sensitivity of the inversion method to underlying assumptions and to ensure robustness of the results. The results indicate a strong seasonal cycle in terrestrial land fluxes from the South Island of New Zealand, especially in western regions covered by indigenous forest, suggesting higher photosynthetic and respiratory activity than is evident in the current a priori land process model. On the annual scale, the terrestrial biosphere in New Zealand is estimated to be a net CO2 sink, removing 98 (±37) Tg CO2 yr−1 from the atmosphere on average during 2011–2013. This sink is much larger than the reported 27 Tg CO2 yr−1 from the national inventory for the same time period. The difference can be partially reconciled when factors related to forest and agricultural management and exports, fossil fuel emission estimates, hydrologic fluxes, and soil carbon change are considered, but some differences are likely to remain. Baseline uncertainty, model transport uncertainty, and limited sensitivity to the northern half of the North Island are the main contributors to flux uncertainty.
Wintertime aerosol chemistry and haze evolution in an extremely polluted city of
North China Plain: significant contribution from coal and biomass combustions
Authors: Li Haiyan , Zhang Qi , Zhang Qiang , Chen Chunrong , Wang Litao , Wei Zhe , Zhou Shan , Parworth Caroline , Zheng Bo , Canonaco Francesco , Prévôt André S. H. , Chen Ping , Zhang Hongliang , He Kebin
Published: January 2017

Abstract. The North China Plain (NCP) frequently encountered heavy haze pollution in recent years, particularly during wintertime. In 2015–2016 winter, the NCP region suffered several extremely severe haze episodes with air pollution red alerts issued in many cities. In this work, we investigated the sources and aerosol evolution processes of the severe pollution episodes in Handan, a typical industrialized city in the NCP region, using real-time measurements from an intensive field campaign during the winter of 2015–2016. The average (± 1σ) concentration of submicron aerosol (PM1) during December 3, 2015–February 5, 2016 was 187.6 (± 137.5) μg m−3, with the hourly maximum reaching 700.8 μg m−3. Organic was the most abundant component, on average accounting for 45 % of total PM1 mass, followed by sulfate (15 %), nitrate (14 %), ammonium (12 %), chloride (9 %) and BC (5 %). Positive matrix factorization (PMF) with multi-linear engine (ME-2) identified four major organic aerosol (OA) sources, including traffic emissions represented by a hydrocarbon-like OA (HOA, 7 % of total OA), industrial and residential burning of coal represented by a coal combustion OA (CCOA, 29 % of total OA), open and domestic combustion of wood and crop residuals represented by a biomass burning OA (BBOA, 25 % of total OA), and formation of secondary OA (SOA) in the atmosphere represented by an oxygenated OA (OOA, 39 % of total OA). Emissions of primary OA (POA), which together accounted for 61 % of total OA and 27 % of PM1, are a major cause of air pollution in this region during the winter. Our analysis further uncovered that, primary emissions from coal combustion and biomass burning together with secondary formation of sulfate (mainly from SO2 emitted by coal combustion) are important driving factors for haze evolution. However, the bulk composition of PM1 showed comparatively small variations between less polluted periods (daily PM2.5 ≤ 75 μg m−3) and severely polluted periods (daily PM2.5 > 75 μg m−3), indicating relatively synchronous increases of all aerosol species during haze formation. The case study of a severe haze episode, which lasted 8 days starting with a steady build-up of aerosol pollution followed by a persistently high level of PM1 (326.7–700.8 μg m−3), revealed the significant influences of stagnant meteorological conditions on acerbating air pollution problems in the Handan region. The haze episode ended with a shift of wind which brought in cleaner air masses from the northwest of Handan and gradually reduced PM1 concentration to
Simultaneous measurements of particle number size distributions at ground level and 260 m on a meteorological tower in urban Beijing, China
Authors: Du Wei , Zhao Jian , Wang Yuying , Zhang Yingjie , Wang Qingqing , Xu Weiqi , Chen Chen , Han Tingting , Zhang Fang , Li Zhanqing , Fu Pingqing , Li Jie , Wang Zifa , Sun Yele
Published: January 2017

Abstract. Despite extensive studies into characterization of particle number size distributions at ground level, real-time measurements above the urban canopy in the megacity of Beijing has never been performed to date. Here we conducted the first simultaneous measurements of size-resolved particle number concentrations at ground level and 260 m in urban Beijing from 22 August to 30 September. Our results showed overall similar temporal variations in number size distributions between ground level and 260 m, yet periods with significant differences were also observed. Particularly, accumulation mode particles were highly correlated (r2 = 0.85) at the two heights while Aitken mode particles presented more differences. Detailed analysis suggests that the vertical differences in number concentrations strongly depended on particle size, and particles with mobility diameter between 100–200 nm generally showed higher concentrations at higher altitudes. Particle growth rates and condensation sinks were also calculated which were 3.2 and 3.6 nm h−1, and 2.8 × 10−2 and 2.9 × 10−2 s−1, at ground level and 260 m, respectively. By linking particle growth with aerosol composition, we found that organics appeared to play an important role in the early stage of the growth (9:00–12:00) while sulfate was also important during the later period. Positive matrix factorization of size-resolved number concentrations identified three common sources at ground level and 260 m including a factor associated with new particle formation and growth events (NPE), and two secondary factors that represent photochemical processing and regional transport, respectively. Cooking emission was found to have a large contribution to small particles, and showed much higher concentration at ground level than 260 m at dinner time. This result has significant implications that investigation of NPE at ground level in megacities needs to consider the influences of local cooking emissions. The impacts of regional emission controls on particle number concentrations were also illustrated. Our results showed that regional emission controls have a dominant impact on accumulation mode particles by decreasing gas precursors and particulate matter loadings, and hence suppressing particle growth. In contrast, the influences on Aitken particles were much smaller due to the enhanced new particle formation (NPF) events.
Four years of atmospheric mercury records in Northwestern
Patagonia (Argentina): potential sources, concentration patterns and
influence of environmental variables observed at the GMOS EMMA
station
Authors: Diéguez Maria C. , Garcia Patricia E. , Bencardino Mariantonia , D'Amore Francesco , Castagna Jessica , Ribeiro Guevara Sergio , Sprovieri Francesca
Published: January 2017

Abstract. The Global Mercury Observation System (GMOS) project, has developed a global-scale network of ground-based atmospheric monitoring sites, expanding the coverage of atmospheric mercury (Hg) measurements worldwide and improving the understanding of global atmospheric Hg transport and deposition, particularly in regions of the South Hemisphere where atmospheric Hg observational data is limited. This work provides the first continuous records of gaseous elemental Hg (GEM) concentrations observed from October 2012 to May 2016 in Northwestern Patagonia (Argentina) at the GMOS EMMA monitoring station (41°7'43.82" S, 71°25'11.89" W, 803 m a.s.l). The monitoring site is located inside Nahuel Huapi National Park, a natural reserve in the Lake District of Andean Patagonia. The area is within the Southern Volcanic Zone, influenced by several active volcanoes aligned in the Andes cordillera. During the studied period, GEM concentrations ranged between 0.23 and 1.43 ng m−3, with an annual mean of 0.9 ± 0.15 ng m−3. GEM records at EMMA station resemble background concentrations measured in Antarctica and other remote locations of the Southern Hemisphere. GEM concentrations showed seasonal variation with mean values higher during spring (0.93 ± 0.13 ng m−3) and winter (0.92 ± 0.10 ng m−3) followed by summer (0.86 ± 0.15 ng m−3) and at last by autumn (0.81 ± 0.15 ng m−3). Further, a clear daily pattern was observed, with higher GEM levels during day-time than at night-time across all seasons. Multivariate analyses showed that GEM levels are chiefly determined by meteorological parameters, and, in particular by the westerly winds which represented the most influential variable on GEM records. In order to investigate the potential impact of natural and/or anthropogenic emission sources as well as the role played by the long-range transport on GEM levels, analyses of HYSPLIT backward trajectories (BWT) were carried out for different periods characterized by low and high GEM concentrations. The BWT analysis highlighted the influence of clean oceanic air masses and also of the local and regional active volcanoes in the Andes cordillera.
Global deposition of total reactive nitrogen oxides from
1996 to 2014 constrained with satellite observations of NO2
columns
Authors: Geddes Jeffrey A. , Martin Randall V.
Published: January 2017

Abstract. Reactive nitrogen oxides (NOy) are a major constituent of the nitrogen deposited from the atmosphere, but observational constraints on their deposition are limited by poor or nonexistent measurement coverage in many parts of the world. Here we apply NO2 observations from multiple satellite instruments (GOME, SCIAMACHY, and GOME-2) to constrain the global deposition of NOy over the last two decades. We accomplish this by producing top-down estimates of NOx emissions from inverse modeling of satellite NO2 columns over 1996–2014, and including these emissions in the GEOS-Chem chemical transport model to simulate chemistry, transport, and deposition of NOy. Our estimates of long-term mean wet nitrate (NO3−) deposition are highly consistent with available measurements in North America, Europe, and East Asia combined (r = 0.83, normalized mean bias = −7 %, N = 136). Likewise, our calculated trends in wet NO3− deposition are largely consistent with the measurements, with 129 of the 136 gridded model-data pairs sharing overlapping 95 % confidence intervals. We find that global mean NOy deposition over 1996–2014 is 56.0 Tg N yr−1, with a minimum in 2006 of 50.5 Tg N and a maximum in 2012 of 60.8 Tg N. Regional trends are large, with opposing signs in different parts of the world. Over 1996 to 2014, NOy deposition decreased by up to 60 % in eastern North America, doubled in regions of East Asia, and declined by 20 % in parts of Western Europe. About 40 % of the global NOy deposition occurs over oceans, with deposition to the North Atlantic Ocean declining and deposition to the northwestern Pacific Ocean increasing. Using the residual between NOx emissions and NOy deposition over specific land regions, we investigate how NOx export via atmospheric transport has changed over the last two decades. Net export from the continental United States decreased substantially, from 2.9 Tg N yr−1 in 1996 to 1.5 Tg N yr−1 in 2014. On the other hand, export from China more than tripled between 1996 and 2011 (from 1.0 Tg N yr−1 to 3.5 Tg N yr−1), before a striking decline to 2.5 Tg N yr−1 by 2014. We find that declines in NOx export from some Western European countries have counteracted increases in emissions from neighbouring countries to the east. A sensitivity study indicates that simulated NOy deposition is robust to uncertainties in NH3 emissions with a few exceptions. Our novel long-term study provides timely context on the rapid redistribution of atmospheric nitrogen transport and subsequent deposition to ecosystems around the world.
Overview of the European framework for online integrated air quality and meteorology modelling (EuMetChem)
Authors: Baklanov Alexander
Published: January 2017

Abstract. The COST Action ES1004 – European framework for online integrated air quality and meteorology modelling (EuMetChem) is focusing on a new generation of online integrated Atmospheric Chemical Transport (ACT) and Meteorology (Numerical Weather Prediction and Climate) models with two-way interactions between different atmospheric processes including chemistry (both gases and aerosols), clouds, radiation, turbulent mixing, emissions, meteorology and climate. Two major application areas of the integrated modelling are considered: (i) improved numerical meteorology and weather prediction (NWP) and chemical weather forecasting (CWF) with short-term feedbacks of aerosols and chemistry on meteorological variables, and (ii) two-way interactions between atmospheric pollution/composition and climate variability/change. The framework consists of 4 working groups namely: 1) Strategy and framework for online integrated modelling; 2) Interactions, parametrizations and feedback mechanisms; 3) Chemical data assimilation in integrated models; and 4) Evaluation, validation, and applications. Establishment of such an European framework (involving also key American experts) enables the EU to develop world class capabilities in integrated ACT/NWP-Climate modelling systems, including research, education and forecasting. This article provides an introduction to the EuMetChem goals and outcomes for this Special Issue "Coupled chemistry–meteorology modelling: status and relevance for numerical weather prediction, air quality and climate communities (SI of EuMetChem COST ES1004)" which collects key scientific papers of EuMetChem and its collaborators from different continents.
Remote sensing of volcanic CO2, HF, HCl, SO2, and BrO in the downwind plume of Mt. Etna
Authors: Butz André , Dinger Anna Solvejg , Bobrowski Nicole , Kostinek Julian , Fieber Lukas , Fischerkeller Constanze , Giuffrida Giovanni Bruno , Hase Frank , Klappenbach Friedrich , Kuhn Jonas , Lübcke Peter , Tirpitz Lukas , Tu Qiansi
Published: January 2017

Abstract. Remote sensing of the gaseous composition of non-eruptive, passively degassing volcanic plumes can be a tool to gain insight into volcano interior processes. Here, we report on a field study in September 2015 that demonstrates the feasibility of remotely measuring the volcanic enhancements of carbon dioxide (CO2), hydrogen fluoride (HF), hydrogen chloride (HCl), sulfur dioxide (SO2), and bromine monoxide (BrO) in the downwind plume of Mt. Etna using portable and rugged spectroscopic instrumentation. To this end, we operated the Fourier transform spectrometer EM27/SUN for the shortwave-infrared (SWIR) spectral range together with a co-mounted UV spectrometer on a mobile platform in direct-sun view at 5 to 10 km distance from the summit craters. The 3 days reported here cover several plume traverses and a sunrise measurement. For all days, intra-plume HF, HCl, SO2, and BrO vertical column densities (VCDs) were reliably measured exceeding 5  × 1016, 2  × 1017, 5  × 1017, and 1  × 1014 molec cm−2, with an estimated precision of 2.2  × 1015, 1.3  × 1016, 3.6  × 1016, and 1.3  × 1013 molec cm−2, respectively. Given that CO2, unlike the other measured gases, has a large and well-mixed atmospheric background, derivation of volcanic CO2 VCD enhancements (ΔCO2) required compensating for changes in altitude of the observing platform and for background concentration variability. The first challenge was met by simultaneously measuring the overhead oxygen (O2) columns and assuming covariation of O2 and CO2 with altitude. The atmospheric CO2 background was found by identifying background soundings via the co-emitted volcanic gases. The inferred ΔCO2 occasionally exceeded 2  ×  1019 molec cm−2 with an estimated precision of 3.7  ×  1018 molec cm−2 given typical atmospheric background VCDs of 7 to 8  ×  1021 molec cm−2. While the correlations of ΔCO2 with the other measured volcanic gases confirm the detection of volcanic CO2 enhancements, correlations were found of variable significance (R2 ranging between 0.88 and 0.00). The intra-plume VCD ratios ΔCO2 ∕ SO2, SO2 ∕ HF, SO2 ∕ HCl, and SO2 ∕ BrO were in the range 7.1 to 35.4, 5.02 to 21.2, 1.54 to 3.43, and 2.9  ×  103 to 12.5  ×  103, respectively, showing pronounced day-to-day and intra-day variability.
High resolution mapping of the NO2 spatial distribution over Belgian urban areas based on airborne APEX remote sensing
Authors: Tack Frederik , Merlaud Alexis , Iordache Marian-Daniel , Danckaert Thomas , Yu Huan , Fayt Caroline , Meuleman Koen , Deutsch Felix , Fierens Frans , Van Roozendael Michel
Published: January 2017

Abstract. We present retrieval results of tropospheric nitrogen dioxide (NO2) vertical column densities (VCDs), mapped at high spatial resolution over three Belgian cities, based on the DOAS analysis of Airborne Prism EXperiment (APEX) observations. APEX, developed by a Swiss-Belgian consortium on behalf of ESA (European Space Agency), is a pushbroom hyperspectral imager characterised by a high spatial resolution and high spectral performance. APEX data have been acquired under clear sky conditions over the three largest and most heavily polluted Belgian cities, i.e. Brussels, Antwerp and Liège on 15 April and 30 June 2015. Additionally, a number of background sites have been covered for the reference spectra. The APEX instrument was mounted in a Dornier DO-228 airplane, operated by Deutsches Zentrum für Luft- und Raumfahrt (DLR). NO2 VCDs were retrieved from spatially aggregated radiance spectra allowing to resolve urban plumes at the resolution of 60 x 80 m2. Main sources in the Antwerp area appear to be related to (petro)chemical industry while traffic-related emissions dominate in Brussels. The NO2 levels observed in Antwerp range between 3 and 35 x 1015 molec m−2, with a mean VCD of 17.4 ± 3.7 x 1015 molec cm−2. In the Brussels area, smaller levels are found, ranging between 1 and 20 x 1015 molec cm−2 and a mean VCD of 7.7 ± 2.1 x 1015 molec cm−2. The overall error on the retrieved N2 VCDs is on average 21 % and 28 % for the Antwerp and Brussels data set, respectively. Low VCD retrievals are mainly limited by noise (1-sigma slant error), while high retrievals are mainly limited by systematic errors. Compared to coincident car mobile-DOAS measurements performed in Antwerp and Brussels, both data sets are in good agreement with correlation coefficients around 0.85 and slopes close to unity. APEX retrievals tend to be on average 12 % and 6 % higher for Antwerp and Brussels, respectively. Results demonstrate that the NO2 distribution in an urban environment, and its fine scale variability, can be mapped accurately with high spatial resolution and in a relatively short time frame, and the contributing emission sources can be resolved. High resolution quantitative information about the atmospheric NO2 horizontal variability is currently rare, but can be very valuable for (air quality) studies at the urban scale.
Simultaneous and synergistic profiling of cloud and drizzle properties using ground-based observations
Authors: Rusli Stephanie P. , Donovan David P. , Russchenberg Herman W. J.
Published: January 2017

Abstract. Despite the importance of radar reflectivity (Z) measurements in the retrieval of liquid water cloud properties, it remains non-trivial to interpret Z due to the possible presence of drizzle droplets within the clouds. So far, there has been no published work that utilizes Z to identify the presence of drizzle above the cloud base in an optimized and a physically-consistent manner. In this work, we develop a retrieval technique that exploits the synergy of different remote sensing systems to carry out this task and to subsequently profile the microphysical properties of the cloud and drizzle in a unified framework. This is accomplished by using ground-based measurements of Z, lidar attenuated backscatter below as well as above the cloud base, and microwave brightness temperatures. Fast physical forward models coupled to cloud and drizzle structure parametrization are used in an optimal estimation type framework in order to retrieve the best-estimate for the cloud and drizzle property profiles. The cloud retrieval is first evaluated using synthetic signals generated from large-eddy simulation output to verify the forward models used in the retrieval procedure and the vertical parametrization of the liquid water content. From this exercise it is found that, on average, the cloud properties can be retrieved within 5 % of the mean truth. The full cloud-drizzle retrieval method is then applied to a selected ACCEPT campaign dataset collected in Cabauw, The Netherlands. An assessment of the retrieval products is performed using three independent methods from the literature, each was specifically developed to retrieve only the cloud properties, the drizzle properties below the cloud base, or the drizzle fraction within the cloud, respectively. One-to-one comparisons, taking into account the uncertainties or limitations of each retrieval, show that our results are generally consistent with what is derived using the three independent methods.
Methods to homogenize ECC ozonesonde measurements across changes in sensing solution concentration or ozonesonde manufacturer
Authors: Deshler Terry , Stübi Rene , Schmidlin Francis J. , Mercer Jennifer L. , Smit Herman G. J. , Johnson Bryan J. , Kivi Rigel , Nardi Bruno
Published: January 2017

Abstract. From the mid 1990s to the late 2000s the consistency of electrochemical cell ozonesonde long term records has been compromised by differences in manufacturers, Science Pump and ENSCI, and differences in recommended sensor solution concentrations, 1.0 % potassium iodide (KI) and the one half dilution 0.5 %. To investigate these differences a number of organizations independently undertook comparisons of the various ozonesonde types and solution concentrations, resulting in 197 ozonesonde comparison profiles. The goal is to derive transfer functions to allow measurements outside of standard recommendations, for sensor composition and ozonesonde type, to be converted to a standard measurement and thus homogenize the data to the expected accuracy of 5 % (10 %) in the stratosphere (troposphere). Subsets of these data have been analyzed previously and intermediate transfer functions derived. Here all the comparison data are analyzed to compare: 1) differences in sensor solution composition for a single ozonesonde type, 2) differences in ozonesonde type for a single sensor solution composition and 3) the manufacturer’s recommendations of 1.0 % KI solution for Science Pump and 0.5 % KI for ENSCI. From the recommendations it is clear that ENSCI ozonesondes and 1.0 % KI solution result in higher amounts of ozone sensed. The results indicate that differences in solution composition and in ozonesonde type display little pressure dependence at pressures ≥ 30 hPa and thus the transfer function can be characterized as a simple ratio of the less sensitive to the more sensitive method. This ratio is 0.96 for both solution concentration and ozonesonde type. The ratios differ at pressures
No significant changes in topsoil carbon in the grasslands of northern China between the 1980s and 2000s
Authors: Liu Shangshi , Yang Yuanhe , Shen Haihua , Hu Huifeng , Zhao Xia , Li He , Liu Taoyu , Fang Jingyun
Published: January 2017

Abstract. The grasslands of northern China store a large amount of soil organic carbon (SOC), and the small changes in SOC stock could significantly affect the regional C cycle. However, recent estimates of SOC changes in this region are highly controversial. In this study, we examined the changes in the SOC density (SOCD) in the upper 30 cm of the grasslands of northern China between the 1980s and 2000s, using an improved approach that integrates field-based measurements into machine learning algorithms (artificial neural network and random forest). The random forest-generated SOCD averaged 5.55 kg C m−2 in the 1980s and 5.53 kg C m−2 in the 2000s. The change ranged between −0.17 and 0.22 kg C m−2 at the 95 % confidence level, suggesting that the overall SOCD did not change significantly during the study period. However, the change in SOCD exhibited large regional variability. The topsoil of the Inner Mongolian grasslands experienced a significant C loss (4.86 vs. 4.33 kg C m-2), whereas that of the Xinjiang grasslands exhibited an accumulation of C (5.55 vs. 6.46 kg C m−2). In addition, the topsoil C in the Tibetan alpine grasslands remained relatively stable (6.12 vs. 6.06 kg C m−2). A comparison of different grassland types indicated that SOCD exhibited significant decreases in typical steppe, whereas showed increases in mountain meadow, and were stable in the remaining grasslands (alpine meadow, alpine steppe, mountain steppe and desert steppe). Climate change could partly explain these changes in the SOCD of the different grassland types. Increases in precipitation could lead to SOC increase in temperate grasslands and SOC loss in alpine grasslands, while climate warming is likely to cause SOC loss in temperate grasslands. Overall, our study shows that northern grasslands in China remained a neutral SOC sink between the 1980s and 2000s.
Isoprenoid emission response to changing light conditions of English
oak, European beech and Norway spruce
Authors: van Meeningen Ylva , Schurgers Guy , Rinnan Riikka , Holst Thomas
Published: January 2017

Abstract. Light is an important environmental factor controlling biogenic volatile organic compound (BVOC) emissions, but in natural conditions its impact is hard to separate from other influential factors such as temperature. We studied the light response of foliar BVOC emissions, photosynthesis and stomatal conductance on three common European tree species, namely English oak (Quercus robur), European beech (Fagus sylvatica) and two provenances of Norway spruce (Picea abies) in Taastrup, Denmark. Leaf scale measurements were performed on the lowest positioned branches of the tree in July 2015. Light intensity was increased in four steps (0, 500, 1000 and 1500 μmol m−2 s−1), whilst other chamber conditions such as temperature, humidity and CO2 levels were fixed. Whereas the emission rate differed between individuals of the same species, the relative contributions of compounds to the total isoprenoid emission remained similar. Whilst some compounds were species specific, the compounds α-pinene, camphene, 3-carene, limonene and eucalyptol were emitted by all of the measured tree species. Some compounds, like isoprene and sabinene, showed an increasing emission response with increasing light intensity, whereas other compounds, like camphene, had no significant emission response to light for most of the measured trees. English oak and European beech showed high light-dependent emission fractions from isoprene and sabinene, but other emitted compounds were light-independent. For the two provenances of Norway spruce, the compounds α-pinene, 3-carene and eucalyptol showed high light-dependent fractions for many of the measured trees. This study highlights differences between compound emissions in their response to a change in light and a possible light independence for certain compounds, which might be valid for a wider range of tree species. This information could be of importance when improving emission models and to further emphasize the discussion regarding light or temperature dependencies for individual compounds across species.
Evaluating the atmospheric drivers leading to the December Flood 2014 in Schleswig-Holstein, Germany
Authors: Schade Nils H.
Published: January 2017

Abstract. Regional analyses of atmospheric conditions that may cause flooding of important transport infrastructure (railway tracks, highways/roads, rivers/channels) and subsequent adaptation measures are part of the Expertennetzwerk initiated by the German Federal Ministry of Transport and Digital Infrastructure (BMVI). As an exemplary case study, the December flood 2014 in Schleswig–Holstein, Germany, was investigated. Atmospheric conditions at the onset of the flood event are described and evaluated with respect to the general weather situation, initial wetness, and event precipitation. Predominantly persistent westerly situations directed several low pressure systems over the North Sea to Schleswig–Holstein during December 2014, accompanied by prolonged rainfall and finally a strong event precipitation in southern Schleswig–Holstein causing several inland gauges to exceed their by then maximum water levels. An additional storm surge hindering drainage of the catchments into the North and Baltic Sea could have been fatal. Results show that the antecedent precipitation index (API) is able to reflect the soil moisture conditions and, in combination with the maximum 3–day precipitation sum (R3d), to capture the two main drivers finally leading to the flood: (1) Initial wetness of north western Schleswig–Holstein, and (2) strong event precipitation in southern and eastern Schleswig–Holstein from 21–23 December while both indices exceeded their respective 5–year return periods. Further, trend analyses show that both API and R3d are increasing while regional patterns match the north eastward shift of cyclone pathways during recent years, leading to higher risk of flooding in Schleswig–Holstein. Within the Expertennetzwerk, investigations of these and further indices/drivers for earth system changes (e.g. wind surge, sea level rise, land cover changes, and others) derived from observations, reanalyses, and regional climate model data are planned for all German coastal areas: Results can be expected to lead to improved adaptation measures to floods under climate change conditions wherever catchments have to be drained and infrastructures and ecosystems may be harmed, e.g. in other Baltic Sea regions.
The polar amplification asymmetry: Role of antarctic surface height
Authors: Salzmann Marc
Published: January 2017

Abstract. Previous studies have attributed an overall weaker (or slower) polar amplification in Antarctica compared to the Arctic to a weaker antarctic surface albedo feedback and also to more efficient ocean heat uptake in the Southern Ocean in combination with antarctic ozone depletion. Here, the role of the antarctic surface height for meridional heat transport and local radiative feedbacks including the surface albedo feedback was investigated based on CO2 doubling experiments in a low resolution coupled climate model. If Antarctica was assumed to be flat, the north-south asymmetry of the zonal mean top of the atmosphere radiation budget was significantly reduced. Doubling CO2 in a flat Antarctica ("flat AA") model setup led to a stronger increase of southern hemispheric poleward atmospheric and oceanic heat transport compared to the base model setup. Based on partial radiative perturbation (PRP) computations it was shown that local radiative feedbacks and an increase of the CO2 forcing in the deeper atmospheric column also contributed to stronger antarctic warming in the flat AA model setup, and the roles of the individual radiative feedbacks are discussed in some detail. A significant fraction (between 24 and 80 % for three consecutive 25-year time slices starting in year 51 and ending in year 126 after CO2 doubling) of the polar amplification asymmetry was explained by the difference in surface height, but the fraction was subject to transient changes, and might to some extent also depend on model uncertainties.
Enacting the contested past: conflict narratives in educational spaces
Authors: Laketa Sunčana , Suleymanova Dilyara
Published: January 2017

Abstract. The article analyzes unfoldings and enactments of narratives on a politically divisive past in educational spaces of two multi-ethnic settings – the Republic of Tatarstan and Bosnia and Herzegovina. We explore how the contested past is represented within official school curricula and how it unfolds in concrete school settings. In each case we have a historic event that is a politically divisive and contentious issue. Though one of these historical events lies far back in history (1552) and the other is more recent (1992–1995), in both cases the contested past is being silenced in the official history curricula. The paper is guided by the following question: in what ways does a past that is muted within a history curriculum continue to speak and structure the relationships of the school present? In order to answer this question, we situate our work within the literature on ethnographies of education, as well as the relatively new but burgeoning field of inquiry on emotional geographies and anthropologies of education. Drawing on ethnographic fieldwork in these two settings, we argue that the narratives on the violent past form and divide national communities not only through divergent views and interpretations of the historic event by the groups involved but also through strong emotional attachments to these narratives. We conclude by calling for a sustained engagement with emotions in educational settings as sites of embodiment that work to negotiate and actively rework top-down educational narratives, especially when considering the processes of identity-building through school spaces.
Improving the inter-hemispheric gradient of total column atmospheric CO2 and CH4 in simulations with the ECMWF semi-Lagrangian atmospheric global model
Authors: Agusti-Panareda Anna , Diamantakis Michail , Bayona Victor , Klappenbach Friedrich , Butz Andre
Published: January 2017

Abstract. It is a widely established fact that standard semi-Lagrangian advection schemes are highly efficient numerical techniques for simulating the transport of atmospheric tracers. However, as they are not formally mass conserving, it is essential to use some method for restoring mass conservation in long time range forecasts. A common approach is to use global mass fixers. This is the case of the semi-Lagrangian advection scheme in the Integrated Forecasting System (IFS) model used by the Copernicus Atmosphere Monitoring Service (CAMS) at the European Centre for Medium-Range Weather Forecasts (ECMWF).Mass fixers are algorithms with substantial differences in complexity and sophistication but in general of low computational cost. This paper shows the positive impact mass fixers have on the inter-hemispheric gradient of total atmospheric column-averaged CO2 and CH4, a crucial feature of their spatial distribution. Two algorithms are compared: the simple "proportional" and the more complex Bermejo–Conde schemes. The former is widely used by several Earth system climate models as well the CAMS global forecasts and analysis of atmospheric composition, while the latter has been recently implemented in IFS. Comparisons against total column observations demonstrate that the proportional mass fixer is shown to be suitable for the low-resolution simulations, but for the high-resolution simulations the Bermejo–Conde scheme clearly gives better results. These results have potential repercussions for climate Earth system models using proportional mass fixers as their resolution increases. It also emphasises the importance of benchmarking the tracer mass fixers with the inter-hemispheric gradient of long-lived greenhouse gases using observations.
CPMIP: measurements of real computational performance of Earth system models in CMIP6
Authors: Balaji Venkatramani , Maisonnave Eric , Zadeh Niki , Lawrence Bryan N. , Biercamp Joachim , Fladrich Uwe , Aloisio Giovanni , Benson Rusty , Caubel Arnaud , Durachta Jeffrey , Foujols Marie-Alice , Lister Grenville , Mocavero Silvia , Underwood Seth , Wright Garrett
Published: January 2017

Abstract. A climate model represents a multitude of processes on a variety of timescales and space scales: a canonical example of multi-physics multi-scale modeling. The underlying climate system is physically characterized by sensitive dependence on initial conditions, and natural stochastic variability, so very long integrations are needed to extract signals of climate change. Algorithms generally possess weak scaling and can be I/O and/or memory-bound. Such weak-scaling, I/O, and memory-bound multi-physics codes present particular challenges to computational performance. Traditional metrics of computational efficiency such as performance counters and scaling curves do not tell us enough about real sustained performance from climate models on different machines. They also do not provide a satisfactory basis for comparative information across models. codes present particular challenges to computational performance. We introduce a set of metrics that can be used for the study of computational performance of climate (and Earth system) models. These measures do not require specialized software or specific hardware counters, and should be accessible to anyone. They are independent of platform and underlying parallel programming models. We show how these metrics can be used to measure actually attained performance of Earth system models on different machines, and identify the most fruitful areas of research and development for performance engineering. codes present particular challenges to computational performance. We present results for these measures for a diverse suite of models from several modeling centers, and propose to use these measures as a basis for a CPMIP, a computational performance model intercomparison project (MIP).
Multivariate Statistical Modelling of Compound Events via Pair-Copula Constructions: Analysis of Floods in Ravenna
Authors: Bevacqua Emanuele , Maraun Douglas , Hobæk Haff Ingrid , Widmann Martin , Vrac Mathieu
Published: January 2017

Abstract. Compound events are multivariate extreme events in which the individual contributing variables may not be extreme themselves, but their joint – dependent – occurrence causes an extreme impact. The conventional univariate statistical analysis cannot give accurate information regarding the multivariate nature of these events. We develop a conceptual model, implemented via pair-copula constructions, which allows for the quantification of the risk associated with compound events in present day and future climate, as well as the uncertainty estimates around such risk. The model includes meteorological predictors which provide insight into both the involved physical processes, and the temporal variability of CEs. Moreover, this model provides multivariate statistical downscaling of compound events. Downscaling of compound events is required to extend their risk assessment to the past or future climate, where climate models either do not simulate realistic values of the local variables driving the events, or do not simulate them at all. Based on the developed model, we study compound floods, i.e. joint storm surge and high river runoff, in Ravenna (Italy). To explicitly quantify the risk, we define the impact of compound floods as a function of sea and river levels. We use meteorological predictors to extend the analysis to the past, and get a more robust risk analysis. We quantify the uncertainties of the risk analysis observing that they are very large due to the shortness of the available data, though this may also be the case in other studies where they have not been estimated. Ignoring the dependence between sea and river levels would result in an underestimation of risk, in particular the expected return period of the highest compound flood observed increases from about 20 to 32 years when switching from the dependent to the independent case.
Spatio-temporal patterns of the effects of precipitation variability and land use/cover changes on long-term changes in sediment yield in the Loess Plateau, China
Authors: Gao Guangyao , Fu Bojie , Sivapalan Murugesu
Published: January 2017

Abstract. Within China's Loess Plateau there have been concerted revegetation efforts and engineering measures over the last 50 years aimed at reducing soil erosion and land degradation. As a result, annual streamflow, sediment yield and sediment concentration have all decreased considerably. Human induced land use/cover change (LUCC) was the dominant factor, contributing over 70 % of the sediment load reduction, with reductions of annual precipitation contributing the remaining 30 %. In this study, we use data on 50-year time series (1961–2011), showing decreasing trends in the annual sediment loads of fifteen catchments, to generate spatio-temporal patterns in the effects of LUCC and precipitation variability on sediment yield. The space-time variability of sediment yield was expressed as a product of two factors representing: (i) effect of precipitation (spatially variable) and (ii) fraction of treated land surface area (temporally variable). Under minimal LUCC, annual sediment yield varied linearly with precipitation, with the precipitation-sediment load relationship showing coherent spatial patterns amongst the catchments. On the other hand, the effect of LUCC is expressed in terms of a sediment coefficient, i.e., ratio of annual sediment yield to annual precipitation, which is equivalent to the slope of the sediment yield-precipitation relationship. Sediment coefficients showed a steady decrease over the study period, following a linear decreasing function of the fraction of treated land surface area. In this way, the study has brought out the separate roles of precipitation variability and LUCC in controlling spatio-temporal patterns of sediment yield at catchment scale.