bluuebunny/crossref_metadata_2025 huggingface dataset:
MODELING SEVEN YEARS OF EVENT HORIZON TELESCOPE OBSERVATIONS WITH RADIATIVELY INEFFICIENT ACCRETION FLOW MODELS
Authors: Broderick Avery E. , Fish Vincent L. , Johnson Michael D. , Rosenfeld Katherine , Wang Carlos , Doeleman Sheperd S. , Akiyama Kazunori , Johannsen Tim , Roy Alan L.
Published: March 2016

An initial three-station version of the Event Horizon Telescope, a millimeter-wavelength very-long baseline interferometer, has observed Sagittarius A* (Sgr A*) repeatedly from 2007 to 2013, resulting in the measurement of a variety of interferometric quantities. Of particular importance is that there is now a large set of closure phases measured over a number of independent observing epochs. We analyze these observations within the context of a realization of semi-analytic radiatively inefficient disk models, implicated by the low luminosity of Sgr A*. We find a broad consistency among the various observing epochs and between different interferometric data types, with the latter providing significant support for this class of model of Sgr A*. The new data significantly tighten existing constraints on the spin magnitude and its orientation within this model context, finding a spin magnitude of

a
=

0.10

−
0.10
−
0.10

+
0.30
+
0.56

, an inclination with respect to the line of sight of

θ
=

60
°

−

8

°

−

13

°

+

5

°

+

10

°

, and a position angle of

ξ
=

156
°

−

17

°

−

27

°

+

10

°

+

14

°

east of north. These are in good agreement with previous analyses. Notably, the previous 180° degeneracy in the position angle has now been conclusively broken by the inclusion of the closure-phase measurements. A reflection degeneracy in the inclination remains, permitting two localizations of the spin vector orientation, one of which is in agreement with the orbital angular momentum of the infrared gas cloud G2 and the clockwise disk of young stars. This may support a relationship between Sgr A*'s accretion flow and these larger-scale features.
CLUSTERING-BASED FEATURE LEARNING ON VARIABLE STARS
Authors: Mackenzie Cristóbal , Pichara Karim , Protopapas Pavlos
Published: March 2016

The success of automatic classification of variable stars depends strongly on the lightcurve representation. Usually, lightcurves are represented as a vector of many descriptors designed by astronomers called features. These descriptors are expensive in terms of computing, require substantial research effort to develop, and do not guarantee a good classification. Today, lightcurve representation is not entirely automatic; algorithms must be designed and manually tuned up for every survey. The amounts of data that will be generated in the future mean astronomers must develop scalable and automated analysis pipelines. In this work we present a feature learning algorithm designed for variable objects. Our method works by extracting a large number of lightcurve subsequences from a given set, which are then clustered to find common local patterns in the time series. Representatives of these common patterns are then used to transform lightcurves of a labeled set into a new representation that can be used to train a classifier. The proposed algorithm learns the features from both labeled and unlabeled lightcurves, overcoming the bias using only labeled data. We test our method on data sets from the Massive Compact Halo Object survey and the Optical Gravitational Lensing Experiment; the results show that our classification performance is as good as and in some cases better than the performance achieved using traditional statistical features, while the computational cost is significantly lower. With these promising results, we believe that our method constitutes a significant step toward the automation of the lightcurve classification pipeline.
THE ORIGIN OF THE COSMIC GAMMA-RAY BACKGROUND IN THE MeV RANGE
Authors: Ruiz-Lapuente Pilar , The Lih-Sin , Hartmann Dieter H. , Ajello Marco , Canal Ramon , Röpke Friedrich K. , Ohlmann Sebastian T. , Hillebrandt Wolfgang
Published: March 2016

There has been much debate about the origin of the diffuse γ-ray background in the MeV range. At lower energies, AGNs and Seyfert galaxies can explain the background, but not above ≃0.3 MeV. Beyond ∼10 MeV blazars appear to account for the flux observed. That leaves an unexplained gap for which different candidates have been proposed, including annihilations of WIMPS. One candidate is Type Ia supernovae (SNe Ia). Early studies concluded that they were able to account for the γ-ray background in the gap, while later work attributed a significantly lower contribution to them. All those estimates were based on SN Ia explosion models that did not reflect the full 3D hydrodynamics of SN Ia explosions. In addition, new measurements obtained since 2010 have provided new, direct estimates of high-z SN Ia rates beyond z ∼ 2. We take into account these new advances to see the predicted contribution to the gamma-ray background. We use here a wide variety of explosion models and a plethora of new measurements of SN Ia rates. SNe Ia still fall short of the observed background. Only for a fit, which would imply ∼150% systematic error in detecting SN Ia events, do the theoretical predictions approach the observed fluxes. This fit is, however, at odds at the highest redshifts with recent SN Ia rate estimates. Other astrophysical sources such as flat-spectrum radio quasars do match the observed flux levels in the MeV regime, while SNe Ia make up to 30%–50% of the observed flux.
ERRATUM: “UTILIZATION OF THE WAVEFRONT SENSOR AND SHORT-EXPOSURE IMAGES FOR SIMULTANEOUS ESTIMATION OF QUASI-STATIC ABERRATION AND EXOPLANET INTENSITY” (ApJ, 767, 21)
Authors: Frazin Richard A.
Published: March 2016

This paper first demonstrates analytically that, at millisecond timescales, the adaptive optics system in a ground-based telescope will maintain the faint planetary emission nearly constant in time, while the speckle intensity at the planet’s location will undergo wild fluctuations. Then, it presents a method for the simultaneous determination of the image of an exo-planetary system and pupil-plane aberrations that are not corrected by the adaptive optics system (so-called “non-common path aberrations”), which cause a confounding speckle background. The central idea of the method is to take simultaneous millisecond exposures in both the wavefront sensor and science camera, and then perform statistical inference procedures to determine both the aberrations and planetary image. The statistical inference is based on a Taylor expansion of an exponential containing the aberration function. While the first order terms given in the paper are correct, it is missing some second-order terms, which are important when the aberrations are large enough so that a first order expansion is not adequate. Since the numerical experiments used small aberrations, this correction has little effect on the results.
DUST DYNAMICS IN PROTOPLANETARY DISK WINDS DRIVEN BY MAGNETOROTATIONAL TURBULENCE: A MECHANISM FOR FLOATING DUST GRAINS WITH CHARACTERISTIC SIZES
Authors: Miyake Tomoya , Suzuki Takeru K. , Inutsuka Shu-ichiro
Published: March 2016

We investigate the dynamics of dust grains of various sizes in protoplanetary disk winds driven by magnetorotational turbulence, by simulating the time evolution of the dust grain distribution in the vertical direction. Small dust grains, which are well-coupled to the gas, are dragged upward with the upflowing gas, while large grains remain near the midplane of a disk. Intermediate-size grains float near the sonic point of the disk wind located at several scale heights from the midplane, where the grains are loosely coupled to the background gas. For the minimum mass solar nebula at 1 au, dust grains with size of 25–45 μm float around 4 scale heights from the midplane. Considering the dependence on the distance from the central star, smaller-size grains remain only in an outer region of the disk, while larger-size grains are distributed in a broader region. We also discuss the implications of our result for observations of dusty material around young stellar objects.
IMAGING A MAGNETIC-BREAKOUT SOLAR ERUPTION
Authors: Chen Yao , Du Guohui , Zhao Di , Wu Zhao , Liu Wei , Wang Bing , Ruan Guiping , Feng Shiwei , Song Hongqiang
Published: March 2016

The fundamental mechanism initiating coronal mass ejections (CMEs) remains controversial. One of the leading theories is magnetic breakout, in which magnetic reconnection occurring high in the corona removes the confinement on an energized low-corona structure from the overlying magnetic field, thus allowing it to erupt. Here, we report critical observational evidence of this elusive breakout reconnection in a multi-polar magnetic configuration that leads to a CME and an X-class, long-duration flare. Its occurrence is supported by the presence of pairs of heated cusp-shaped loops around an X-type null point and signatures of reconnection inflows. Other peculiar features new to the breakout picture include sequential loop brightening, coronal hard X-rays at energies up to ∼100 keV, and extended high-corona X-rays above the later restored multi-polar structure. These observations, from a novel perspective with clarity never achieved before, present crucial clues to understanding the initiation mechanism of solar eruptions.
Evaluating population and community structure against climate and land-use determinants to improve the conservation of the rare Narcissus pseudonarcissus subsp. nobilis
Authors: Vaz Ana Sofia , Silva Duarte , Alves Paulo , Vicente Joana Raquel , Barreto Caldas Francisco , Pradinho Honrado João , Lomba Angela
Published: March 2016

Climate and land-use changes are among the most relevant determinants of future persistence of rare plant species in rural landscapes. We analysed the structure of populations of a rare plant, Narcissus pseudonarcissus subsp. nobilis, and of their respective plant communities against several environmental variables (climate-, topography-, land-use-, and soil-related) in order to identify the pressures that may directly or indirectly affect the persistence of the rare species. Overall, local land-use was the primary determinant of traits related to population renewal and community composition. Specifically, traditional farmlands supported higher community diversity and population individuals. Though moderate land-use intensification seemed to benefit plant community diversity, land abandonment could allow the persistence of N. pseudonarcissus subsp. nobilis populations. Also, a relevant influence of regional environment was perceived on species richness as well as on traits related to population condition, highlighting climate change as a potential determinant of the future persistence of the species. This study highlights the importance of considering key population traits as well as of community structure to accomplish conservation goals by accounting with the factors driving changes in the habitats in which rare species occur, from climate change to land-use and landscape management.
Updated taxonomic descriptions, iconography, and habitat preferences of Brachypodium distachyon, B. stacei, and B. hybridum (Poaceae)
Authors: Catalán Pilar , López-Álvarez Diana , Bellosta Cristina , Villar Luis
Published: March 2016

We present an updated morphological revision of the three annual species of the genus Brachypodium (Poaceae): B. distachyon, B. tacei, and B. hybridum, which were recently segregated as independent species from the single-species complex B. distachyon s.l. These three species have been proposed as a model system for grass polyploid speciation, and their genomes have been sequenced. However, despite the increasing number of genomic and population-genetic studies conducted for each of these species, no taxonomic updating has been done on them since their original descriptions. B. stacei, the rarest species of the complex, has a protologue based only on the study of specimens from its type locality in Torrent (Formentera, Spain). In this study we update the taxonomic descriptions of the three species using morphoanatomical data from specimens collected throughout their respective native circum-Mediterranean distributions as well as in other localities where they are non-autochthonous. We also provide icons for each species and information about their habitat preferences and geographic distributions.
Utilizing Communities of Practice to Facilitate Knowledge Sharing in the Digital Age
Authors: Kasemsap Kijpokin
Published: March 2016

This chapter explains the overview of knowledge sharing; the perspectives of knowledge sharing behavior; the barriers to knowledge sharing; the overview of communities of practice (CoPs); the relationships among CoPs, knowledge sharing, and information technology; and the utilization of CoPs to facilitate knowledge sharing in the digital age. CoPs can create the valuable opportunities for members to explicitly discuss the productivity of their participation in the group toward sharing knowledge in modern business. The strong CoPs facilitate the social interactions and encourage the members' willingness to share knowledge and ideas in the workplace. CoPs help promote a growing cycle of knowledge sharing activities that allow for the members to regularly meet, reflect, and evolve in the knowledge management (KM) environment. The chapter argues that utilizing CoPs to facilitate knowledge sharing has the potential to improve organizational performance and reach strategic goals in the digital age.
Application of UBD Technology for Basement Drilling in Malaysia
Authors: Arathoon Mark
Published: March 2016

The objective of applying underbalanced drilling (UBD) technology to drill basement plays in Malaysia was to determine the true, undamaged production capability, and at the same time determine productivity index while drilling, in order to characterise the reservoir inflow performance versus depth. Previous exploration and appraisal wells had determined oil flow from the basement, but at lower than expected rates, with the understanding that this was due to formation damage.

The key approach was to maintain bottom-hole pressure below formation pressure while drilling. The lower boundary of the formation pressure uncertainty range was hydrostatic pressure. Therefore, the drilling system had to be sub-hydrostatic to ensure underbalanced conditions and eliminate the risk of creating formation damage. Two fluid choices were suitable from a density perspective, base oil and nitrified water. The latter was selected because it enabled simplified separation, avoiding the risk of live oil being returned to the rig pits.

The well design was conventional down to the top of the reservoir, with 9-5/8? liner set 10m inside fresh basement. A tieback liner was run to improve annular velocity and facilitate running a downhole isolation valve to provide improved well integrity and faster bit trips. At first, nitrified seawater was used. However, this was changed to nitrified drillwater to reduce corrosion and scale. Membrane nitrogen was selected on both wells to avoid logistical constraints of supplying cryogenic nitrogen. Two UBD wells were drilled; the first experienced problems with the tieback liner, which backed off while drilling. The liner was re-run and cemented in place to eliminate the risk of recurrence. This approach was repeated on the second well. Although underbalanced conditions were maintained throughout the basement, there was no influx while drilling, or during a subsequent 1000psi drawdown test that was performed with the final drilling BHA. The ROP and bit life exceeded all expectations and demonstrated one of the recognised benefits of UBD. Although oil staining was visible on sidewall cores, it was determined that there were insufficient open and connected fractures to enable the well to flow. The drawdown test was conclusive in avoiding potential additional expenditure on a well test.

These wells demonstrate that basement wells in Malaysia can be successfully drilled using UBD technology and that qualitative reservoir performance information can be obtained while drilling, allowing optimal decision making. From worldwide UBD experience, key benefits include faster ROP, longer bit life, early reservoir characterisation and enhanced productivity. The first three of these have been demonstrated on this project, while the last would still be expected if drilling into open and connected fracture zones.
Chart review of acute myocardial infarction at a district hospital in KwaZulu-Natal, South Africa
Authors: Chetty Roland , Ross Andrew
Published: March 2016

Background: Incidence and prevalence of non-communicable diseases, including ischaemic heart disease (IHD) and associated acute myocardial infarction (AMI), are increasing in South Africa. Local studies are needed as contextual factors, such as healthcare systems, gender and ethnicity, may affect presentation and management. In AMI, reviews on time between onset of chest pain and initiation of urgent treatment are useful, as delays in initiation of thrombolytic treatment significantly increase morbidity and mortality.Aim: The aim of the study was to determine the profile and management of patients admitted with ischaemic chest pain.Setting: The study was carried out in a busy urban-based district hospital in KwaZulu-Natal, South Africa. The population served is poor, and patients are mainly Indian with associated high risk of IHD.Methods: A chart review of all patients seen at the hospital with acute ischaemic chest pain between 01 March and 31 August 2014 was undertaken.Results: More male than female patients were admitted, with a wide variation in age. Most eligible patients received required thrombolytic intervention within an acceptable time period after arrival at hospital.Conclusion: Chest pain and AMI were a relatively common presentation at the study site, and urgent diagnosis and initiation of fibrinolytic therapy are essential. The encouraging door-toneedle time may have been influenced by the availability of specialist family physicians, trained as ‘expert generalists’ to provide appropriate care in a variety of settings and consultant support to junior staff. The role of the family physician and primary healthcare doctor in primary prevention are re-emphasised through the study findings.Keywords: Acute myocardial infarction; KwaZulu-Natal; district hospital; Asian population; hospital chart review; door-to-needle-time
3D-Printing in Congenital Cardiology: From Flatland to Spaceland
Authors: Deferm Sébastien , Meyns Bart , Vlasselaers Dirk , Budts Werner
Published: March 2016

Medical imaging has changed to a great extent over the past few decades. It has been revolutionized by three-dimensional (3D) imaging techniques. Despite much of modern medicine relying on 3D imaging, which can be obtained accurately, we keep on being limited by visualization of the 3D content on two-dimensional flat screens. 3D-printing of graspable models could become a feasible technique to overcome this gap. Therefore, we printed pre- and postoperative 3D-models of a complex congenital heart defect. With this example, we intend to illustrate that these models hold value in preoperative planning, postoperative evaluation of a complex procedure, communication with the patient, and education of trainees. At this moment, 3D printing only leaves a small footprint, but makes already a big impression in the domain of cardiology and cardiovascular surgery. Further studies including more patients and more validated applications are needed to streamline 3D printing in the clinical setting of daily practice.
Sonographic Appearance of the Median Nerve Following Revision Carpal Tunnel Surgery
Authors: Shapiro Shane A , Alkhamisi Ashkan , Pujalte George G A
Published: March 2016

The main objective of this pictorial essay is to illustrate the sonographic appearance of the postoperative carpal tunnel and median nerve. Carpal tunnel surgical treatment failures have been shown to occur in up to 19% of a large series requiring re-exploration. Surgical management options for recurrent carpal tunnel syndrome (CTS) include revision release, neurolysis, vein wrapping, and fat grafting procedures. While several descriptions of median nerve entrapment in CTS exist in the ultrasound literature, little is written regarding its postoperative appearance. We report the sonographic changes in the appearance of the median nerve and postoperative carpal tunnel.
Impact of a Saharan dust outbreak on PM10 ground levels in Southeastern France
Authors: Michelot Nicolas , Endlicher Wilfried , Carrega Pierre , Martin Nicolas , Favez Olivier , Langner Marcel
Published: March 2016

Southeastern France is often subject to thermal breezes and inversions that are partly responsible for the dispersion behavior of air pollutants in this region. Generally, the coastal urban zone is the main contributor to PM10 emissions. However, a southerly wind, commonly known as Sirocco, occasionally generates dust advections from the Sahara desert, resulting in poor air quality in the study area. This work demonstrates the quick rise of PM10 levels on the French coastline under the influence of such a weather outbreak. Measurements were performed during a Saharan dust episode which occurred end of April 2013 and caused the tripling of PM10 daily averages at the regional scale in about 24 hours. In Vence, located in the Alpes-Maritimes department, the highest daily average was 7 times greater during the peak than before the dust outbreak. In Venaco (Corsica) off-line chemical characterizations for filter samples show that about 50% of the PM10 mass was composed of terrigenous dust, which confirms that they played a central role in the degradation of air quality and in the exceeding of the EU daily limit value of 50 μg/m3 at a regional scale.
Tropospheric mercury vertical profiles between 500 and 10 000 m in central Europe
Authors: Weigelt Andreas , Ebinghaus Ralf , Pirrone Nicola , Bieser Johannes , Bödewadt Jan , Esposito Giulio , Slemr Franz , van Velthoven Peter F. J. , Zahn Andreas , Ziereis Helmut
Published: March 2016

Abstract. The knowledge of the vertical distribution of atmospheric mercury (Hg) plays an important role in determining the transport and cycling of mercury. However, measurements of the vertical distribution are rare, because airborne measurements are expensive and labour intensive. Consequently, only a few vertical Hg profile measurements have been reported since the 1970s. Besides the Civil Aircraft for the Regular Investigation of the atmosphere Based on an Instrument Container (CARIBIC) observations, the latest vertical profile over Europe was measured in 1996. Within the Global Mercury Observation System (GMOS) project, four vertical profiles were taken on board research aircraft (CASA-212) in August 2013 in background air over different locations in Slovenia and Germany. Each vertical profile consists of at least seven 5 min horizontal flight sections from 500 m above ground to 3000 m a.s.l. Gaseous elemental mercury (GEM) and total gaseous mercury (TGM) were measured with Tekran 2537X and Tekran 2537B analysers. In addition to the mercury measurements, SO2, CO, O3, NO, and NO2, basic meteorological parameters (pressure, temperature, relative humidity) have been measured. Additional ground-based mercury measurements at the GMOS master site in Waldhof, Germany and measurements onboard the CARIBIC passenger aircraft were used to extend the profile to the ground and upper troposphere respectively. No vertical gradient was found inside the well-mixed boundary layer (variation of less than 0.1 ng m−3) at different sites, with GEM varying from location to location between 1.4 and 1.6 ng m−3 (standard temperature and pressure, STP: T  =  273.15 K, p  =  1013.25 hPa). At all locations GEM dropped to 1.3 ng m−3 (STP) when entering the free troposphere and remained constant at higher altitudes. The combination of the vertical profile, measured on 21 August 2013 over Leipzig, Germany, with the CARIBIC measurements during ascent and descent to Frankfurt Airport, Germany, taken at approximately the same time, provide a unique central European vertical profile from inside the boundary layer (550 m a.s.l) to the upper free troposphere (10 500 m a.s.l.) and show a fairly constant free-tropospheric TGM concentration of 1.3 ng m−3 (STP).
Upper tropospheric humidity changes under constant relative humidity
Authors: Gierens Klaus , Eleftheratos Kostas
Published: March 2016

Abstract. Theoretical derivations are given on the change of upper tropospheric humidity (UTH) in a warming climate. The considered view is that the atmosphere, which is getting moister with increasing temperatures, will retain a constant relative humidity. In the present study, we show that the upper tropospheric humidity, a weighted mean over a relative humidity profile, will change in spite of constant relative humidity. The simple reason for this is that the weighting function that defines UTH changes in a moister atmosphere. Through analytical calculations using observations and through radiative transfer calculations, we demonstrate that two quantities that define the weighting function of UTH can change: the water vapour scale height and the peak emission altitude. Applying these changes to real profiles of relative humidity shows that absolute UTH changes typically do not exceed 1 %. If larger changes would be observed they would be an indication of climatological changes of relative humidity. As such, an increase in UTH between 1980 and 2009 in the northern midlatitudes, as shown by earlier studies using the High-resolution Infrared Radiation Sounder (HIRS) data, may be an indication of an increase in relative humidity as well.
Impacts of the 2014–2015 Holuhraun eruption on the UK atmosphere
Authors: Twigg Marsailidh M. , Ilyinskaya Evgenia , Beccaceci Sonya , Green David  C. , Jones Matthew R. , Langford Ben , Leeson Sarah R. , Lingard Justin J. N. , Pereira Gloria M. , Carter Heather , Poskitt Jan , Richter Andreas , Ritchie Stuart , Simmons Ivan , Smith Ron I. , Tang Y. Sim , Van Dijk Netty , Vincent Keith , Nemitz Eiko , Vieno Massimo , Braban Christine F.
Published: March 2016

Abstract. Volcanic emissions, specifically from Iceland, pose a pan-European risk and are on the UK National Risk Register due to potential impacts on aviation, public health, agriculture, the environment and the economy, both from effusive and explosive activity. During the 2014–2015 fissure eruption of the Holuhraun in Iceland, the UK atmosphere was significantly perturbed. This study focuses on the first four months of the eruption (September to December 2014). During this period there was one major incursion in September 2014, affecting the surface concentrations of both aerosols and gases across the UK, with sites in Scotland experiencing the highest sulfur dioxide (SO2) concentrations. At the two UK EMEP supersite observatories (Auchencorth Moss, SE Scotland and Harwell, SE England) significant alterations in sulfate (SO42−) content of PM10 and PM2.5 during this event, concurrently with evidence of an increase in ultrafine aerosol, most likely due to nucleation and growth of aerosol within the plume, were observed. At Auchencorth Moss, higher hydrochloric acid (HCl) concentrations during the September event (max = 1.21 µg m−3, c.f annual average 0.12 µg m−3 in 2013), were assessed to be due to acid displacement of chloride (Cl−) from sea salt (NaCl) to form HCl gas rather than due to primary emissions HCl from Holuhraun. The gas and aerosol partioning at Auchencorth moss of inorganic species by thermodynamic modelling, confirmed the observed partioning of HCl. Volcano plume episodes were observed by the majority of the UK air quality monitoring networks during the first 4 months, at both hourly and monthly resolution. In the monthly networks, SO2 concentrations were significantly elevated at remote "clean" sites in NE Scotland and SW England, with record high SO2 concentrations for some sites. For sites which are regularly influenced by anthropogenic emissions, taking into account the underlying trends, the eruption led to statistically unremarkable SO2 concentrations (return probabilities > 0.1, ~ 10 months). However for a few sites, SO2 concentrations were clearly were much higher than has been previously observed (return probability < 0.005, > 3000 months). The Icelandic eruption has resulted in a unique study providing direct evidence of atmospheric chemistry perturbation of both gases and aerosols in the UK background atmosphere. The measurements can be used to both challenge and verify existing atmospheric chemistry of volcano plumes. If all European data sets were collated this would allow improved model verification and risk assessments for future volcanic eruptions.
Carbon isotopic signature of coal-derived methane emissions to atmosphere: from coalification to alteration
Authors: Zazzeri Giulia , Lowry Dave , Fisher Rebecca E. , France James , Lanoisellé Mathias , Kelly Bryce F. J. , Necki Jaroslaw  M. , Iverach Charlotte P. , Ginty Elisa , Zimnoch Miroslaw , Jasek Alina , Nisbet Euan  G.
Published: March 2016

Abstract. Currently, the atmospheric methane burden is rising rapidly, but the extent to which shifts in coal production contribute to this rise is not known. Coalbed methane emissions into the atmosphere are poorly characterised, and this study provides representative δ13CCH4 signatures to be used in regional and global models in order to allow better apportionment of fossil fuel emissions. Integrated methane emissions from both underground and opencast coal mines in the UK, Australia and Poland were sampled and isotopically characterised. Progression in coal rank and secondary biogenic production of methane due to incursion of water are suggested as the processes affecting the isotopic composition of coal-derived methane. An averaged value of −65 ‰ has been assigned to bituminous coal exploited in open cast mines and of −55 ‰ in deep mines, whereas values of −40 ‰ and −30 ‰ can be allocated to anthracite opencast and deep mines respectively. However, the isotopic signatures that are included in global atmospheric modelling of coal emissions should be region or nation specific, as greater detail is needed, given the wide global variation in coal type.
Hydrometeor classification through statistical clustering of polarimetric radar measurements: a semi-supervised approach
Authors: Besic Nikola , Figueras i Ventura Jordi , Grazioli Jacopo , Gabella Marco , Germann Urs , Berne Alexis
Published: March 2016

Abstract. Hydrometeor classification is the procedure of identifying different types of hydrometeors by exploiting polarimetric radar observations. The main drawback of the existing supervised classification methods, mostly based on fuzzy logic, is a significant dependency on a presumed electromagnetic behavior of different hydrometeor types. Namely, the results of classification largely rely upon the quality of scattering simulations. When it comes to the unsupervised approach, it eventually lacks the constraints related to the hydrometeor microphysics. The idea of the proposed method is to compensate for these drawbacks by combining the two approaches in a way that microphysical hypotheses can, to a degree, adjust the content of the classes obtained statistically from the observations. This is done by means of an iterative approach which, in a statistical framework, examines clustered representative polarimetric observations by comparing them to the presumed polarimetric properties of hydrometeor classes. Aside from comparing, a routine alters the content of clusters by encouraging further statistical clustering in case of non-identification. By merging all identified clusters, the multi-dimensional polarimetric signatures of various hydrometeor types are obtained for each of the studied representative datasets, i.e. for each radar system of interest. These are depicted by sets of centroids which are finally employed in operational labeling of different hydrometeors. The method has been applied on three C-band datasets, each acquired by different operational radar from the MeteoSwiss Rad4Alp network, as well as on an X-band dataset acquired by a research radar. The results are discussed through a comparative analysis which includes a corresponding supervised and unsupervised approach, with a particular emphasis on hail detection performances.
Re-evaluating the Frankfurt isothermal static diffusion chamber for ice nucleation
Authors: Schrod Jann , Danielczok Anja , Weber Daniel , Ebert Martin , Thomson Erik S. , Bingemer Heinz G.
Published: March 2016

Abstract. Recently significant advances have been made in the collection, detection and characterization of ice nucleating particles (INPs). Ice nuclei are particles that facilitate the heterogeneous formation of ice within the atmospheric aerosol by lowering the free energy barrier to spontaneous nucleation and growth of ice from atmospheric water and/or vapor. The Frankfurt isostatic diffusion chamber (FRankfurt Ice nucleation Deposition freezinG Experiment: FRIDGE) is an INP collection and offline detection system that has become widely deployed and shows additional potential for ambient measurements. Since its initial development FRIDGE has gone through several iterations and improvements. Here we describe improvements that have been made in the collection and analysis techniques. We detail the uncertainties inherent in the measurement method and suggest a systematic method of error analysis for FRIDGE measurements. Thus what is presented herein should serve as a foundation for the dissemination of all current and future measurements using FRIDGE instrumentation.
Proximate and ultimate controls on carbon and nutrient dynamics of small agricultural catchments
Authors: Thomas Zahra , Abbott Benjamin W. , Troccaz Olivier , Baudry Jacques , Pinay Gilles
Published: March 2016

Abstract. Direct and indirect effects from human activity have dramatically increased nutrient loading to aquatic inland and estuarine ecosystems. Despite an abundance of studies investigating the impact of agricultural activity on water quality, our understanding of what determines the capacity of a watershed to remove or retain nutrients remains limited. The goal of this study was to identify proximate and ultimate controls on dissolved organic carbon and nutrient dynamics in small agricultural catchments by investigating the relationship between catchment characteristics, stream discharge, and water chemistry. We analyzed a 5-year, high-frequency water chemistry data set from three catchments in western France ranging from 2.3 to 10.8 km2. The relationship between hydrology and solute concentrations differed between the three catchments and was associated with hedgerow density, agricultural activity, and geology. The catchment with thicker soil and higher surface roughness had relatively invariant carbon and nutrient chemistry across hydrologic conditions, indicating high resilience to human disturbance. Conversely, the catchments with smoother, thinner soils responded to both intra- and interannual hydrologic variation with high concentrations of phosphate (PO43−) and ammonium (NH4+) in streams during low flow conditions and strong increases in dissolved organic carbon (DOC), sediment, and particulate organic matter during high flows. Despite contrasting agricultural activity between catchments, the physical context (geology, topography, and land-use configuration) appeared to be the most important determinant of catchment solute dynamics based on principle components analysis. The influence of geology and accompanying topographic and geomorphological factors on water quality was both direct and indirect because the distribution of agricultural activity in these catchments is largely a consequence of the geologic and topographic context. This link between inherent catchment buffering capacity and the probability of human disturbance provides a useful perspective for evaluating vulnerability of aquatic ecosystems and for managing systems to maintain agricultural production while minimizing leakage of nutrients.
Low methane (CH4) emissions downstream of a monomictic subtropical hydroelectric reservoir (Nam Theun 2, Lao PDR)
Authors: Deshmukh Chandrashekhar , Guérin Frédéric , Labat David , Pighini Sylvie , Vongkhamsao Axay , Guédant Pierre , Rode Wanidaporn , Godon Arnaud , Chanudet Vincent , Descloux Stéphane , Serça Dominique
Published: March 2016

Abstract. Methane (CH4) emissions from hydroelectric reservoirs could represent a significant fraction of global CH4 emissions from inland waters and wetlands. Although CH4 emissions downstream of hydroelectric reservoirs are known to be potentially significant, these emissions are poorly documented in recent studies. We report the first quantification of emissions downstream of a subtropical monomictic reservoir. The Nam Theun 2 Reservoir (NT2R), located in the Lao People's Democratic Republic, was flooded in 2008 and commissioned in April 2010. This reservoir is a trans-basin diversion reservoir which releases water into two downstream streams: the Nam Theun River below the dam and an artificial channel downstream of the powerhouse and a regulating pond that diverts the water from the Nam Theun watershed to the Xe Bangfai watershed. We quantified downstream emissions during the first 4 years after impoundment (2009–2012) on the basis of a high temporal (weekly to fortnightly) and spatial (23 stations) resolution of the monitoring of CH4 concentration. Before the commissioning of NT2R, downstream emissions were dominated by a very significant degassing at the dam site resulting from the occasional spillway discharge for controlling the water level in the reservoir. After the commissioning, downstream emissions were dominated by degassing which occurred mostly below the powerhouse. Overall, downstream emissions decreased from 10 GgCH4 yr−1 after the commissioning to 2 GgCH4 yr−1 4 years after impoundment. The downstream emissions contributed only 10 to 30 % of total CH4 emissions from the reservoir during the study. Most of the downstream emissions (80 %) occurred within 2–4 months during the transition between the warm dry season (WD) and the warm wet season (WW) when the CH4 concentration in hypolimnic water is maximum (up to 1000 µmol L−1) and downstream emissions are negligible for the rest of the year. Emissions downstream of NT2R are also lower than expected because of the design of the water intake. A significant fraction of the CH4 that should have been transferred and emitted downstream of the powerhouse is emitted at the reservoir surface because of the artificial turbulence generated around the water intake. The positive counterpart of this artificial mixing is that it allows O2 diffusion down to the bottom of the water column, enhancing aerobic methane oxidation, and it subsequently lowered downstream emissions by at least 40 %.
Carbon sequestration in managed temperate coniferous forests under climate change
Authors: Dymond Caren C. , Beukema Sarah , Nitschke Craig R. , Coates K. David , Scheller Robert M.
Published: March 2016

Abstract. Management of temperate forests has the potential to increase carbon sinks and mitigate climate change. However, those opportunities may be confounded by negative climate change impacts. We therefore need a better understanding of climate change alterations to temperate forest carbon dynamics before developing mitigation strategies. The purpose of this project was to investigate the interactions of species composition, fire, management, and climate change in the Copper–Pine Creek valley, a temperate coniferous forest with a wide range of growing conditions. To do so, we used the LANDIS-II modelling framework including the new Forest Carbon Succession extension to simulate forest ecosystems under four different productivity scenarios, with and without climate change effects, until 2050. Significantly, the new extension allowed us to calculate the net sector productivity, a carbon accounting metric that integrates aboveground and belowground carbon dynamics, disturbances, and the eventual fate of forest products. The model output was validated against literature values. The results implied that the species optimum growing conditions relative to current and future conditions strongly influenced future carbon dynamics. Warmer growing conditions led to increased carbon sinks and storage in the colder and wetter ecoregions but not necessarily in the others. Climate change impacts varied among species and site conditions, and this indicates that both of these components need to be taken into account when considering climate change mitigation activities and adaptive management. The introduction of a new carbon indicator, net sector productivity, promises to be useful in assessing management effectiveness and mitigation activities.
Automation of soil flux chamber measurements: potentials and pitfalls
Authors: Görres Carolyn-Monika , Kammann Claudia , Ceulemans Reinhart
Published: March 2016

Abstract. Recent technological advances have enabled the wider application of automated chambers for soil greenhouse gas (GHG) flux measurements, several of them commercially available. However, few studies addressed the challenges associated with operating these systems. In this contribution we compared two commercial soil GHG chamber systems – the LI-8100A Automated Soil CO2 Flux System and the greenhouse gas monitoring system AGPS. From April until August 2014, the two systems monitored in parallel soil respiration (SR) fluxes at a recently harvested poplar (Populus) plantation, which provided a bare field situation directly after the harvest as well as a closed canopy later on. For the bare field situation (15 April–30 June 2014), the cumulated average SR obtained from the unfiltered data sets of the LI-8100A and the AGPS were 520 and 433 g CO2 m−2 respectively. For the closed canopy phase (1 July–31 August 2014), which was characterized by a higher soil moisture content, the cumulated average SR estimates were not significantly different with 507 and 501 g CO2 m−2 for the AGPS and the LI-8100A respectively. Flux quality control and filtering did not significantly alter the results obtained by the LI-8100A, whereas the AGPS SR estimates were reduced by at least 20 %. The main reasons for the observed differences in the performance of the two systems were (i) a lower data coverage provided by the AGPS due to technical problems; (ii) incomplete headspace mixing in the AGPS chambers; (iii) lateral soil CO2 diffusion below the collars during AGPS chamber measurements; and (iv) a possible overestimation of nighttime SR fluxes by the LI-8100A. Additionally, increased root growth was observed within the LI-8100A collars but not within the AGPS collars, which might have also contributed to the observed differences. In contrast to the LI-8100A, the AGPS had the gas sample inlets installed inside the collars and not the chambers. This unique design feature enabled for the first time the detection of disturbed chamber measurements during nights with a stratified atmosphere, resulting in unbiased nighttime SR estimates. Thus besides providing high temporal frequency flux data, automated chamber systems offer another possibility to greatly improve our understanding of SR fluxes.
Lava flow hazard at Fogo Volcano, Cape Verde, before and after the 2014–2015 eruption
Authors: Richter Nicole , Favalli Massimiliano , de Zeeuw-van Dalfsen Elske , Fornaciai Alessandro , Fernandes Rui Manuel da Silva , Perez Rodriguez Nemesio , Levy Judith , Victória Sónia Silva , Walter Thomas R.
Published: March 2016

Abstract. Lava flow simulations help to better understand volcanic hazards and may assist emergency preparedness at active volcanoes. We show that at Fogo Volcano, Cape Verde, such simulations can explain the 2014–2015 lava flow crisis and therefore provide a valuable base to better prepare for the inevitable next eruption. In a rapid disaster response effort, we conducted topographic mapping in the field and a satellite based remote sensing analysis. We produced the first topographic model of the 2014–2015 lava flows from combined Terrestrial Laser Scanner (TLS) and photogrammetric data. This high resolution topographic information facilitates lava flow volume estimates of 43.7 × 106 m3 (+/−5.2 × 106 m3) from the vertical difference between pre- and post-eruptive topographies. Both, the pre-eruptive and updated Digital Elevation Models (DEMs) serve as the fundamental input parameters for lava flow simulations using the well-established DOWNFLOW algorithm. Based on thousands of simulations, we assess the lava flow hazard before and after the 2014–2015 eruption. We find that, although the lava flow hazard has changed significantly, it remains high at the locations of two villages that were destroyed during this eruption. This result is of particular importance as villagers have already started to rebuild the settlements. We also analyse satellite radar imagery acquired by the German TerraSAR-X (TSX) satellite to map lava flow emplacement over time. We obtain the lava flow boundaries every 6 days during the eruption which assists the interpretation and evaluation of the lava flow model performance. Based on this, we discuss how our study can help improving the general understanding of basaltic lava flow behavior. Our results highlight the fact that lava flow hazards change as a result of modifications of the local topography due to lava flow emplacement, which implies the need for up-to-date topographic information in order to assess lava flow hazards. We also emphasize that areas that were once overrun by lava flows are not necessarily "safer", even if local lava flow thicknesses exceed the average lava flow thickness. Our observations will be important for the next eruption of Fogo Volcano and have implications for future lava flow crises and disaster response efforts at basaltic volcanoes elsewhere in the world.
Spatio-temporal evolution of snow depth observed by time-lapse laser scanning in the Alps and in Antarctica
Authors: Picard Ghislain , Arnaud Laurent , Panel Jean-Michel , Morin Samuel
Published: March 2016

Abstract. Although both the temporal and spatial variations of the snow depth are usually of interest for numerous applications, available measurement techniques are either space-oriented (e.g. terrestrial laserscans) or time-oriented (e.g. ultrasonic ranging probe). Because of snow heterogeneity, measuring depth in a single point is insufficient to provide accurate and representative estimates. We present a cost-effective automatic instrument to acquire spatio-temporal variations of snow depth. The device comprises a lasermeter mounted on a two-axis stage and can scan ≈ 200,000 points over an area of 100–200 m2 in 4 hours. Two copies, installed in Antarctica and in the French Alps, have been operating daily, unattended over 2015 with a success rate of 65 % and 90 % respectively. The precision of single point measurements and long-term stability were evaluated to be about 1 cm and the accuracy to be 5 cm or better. The spatial variability in the scanned area reached 7–10 cm (root mean square) at both sites, which means that the number of measurements is sufficient to average out the spatial variability and yield precise mean snow depth. With such high precision, it was possible for the first time at Dome C 1) to observe a 3-month period of regular and slow increase of snow depth disconnected from snowfalls and 2) to highlight that most of the annual accumulation stems from a single event although several snowfall and strong wind events were predicted by the ERA-Interim reanalysis. At last the paper discusses the benefit of the RLS solution compared to multiplying single-point sensors in the context of monitoring snow depth.