| 1. |
- Acharya, B. S., et al.
(författare)
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Introducing the CTA concept
- 2013
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Ingår i: Astroparticle physics. - : Elsevier BV. - 0927-6505 .- 1873-2852. ; 43, s. 3-18
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The Cherenkov Telescope Array (CTA) is a new observatory for very high-energy (VHE) gamma rays. CTA has ambitions science goals, for which it is necessary to achieve full-sky coverage, to improve the sensitivity by about an order of magnitude, to span about four decades of energy, from a few tens of GeV to above 100 TeV with enhanced angular and energy resolutions over existing VHE gamma-ray observatories. An international collaboration has formed with more than 1000 members from 27 countries in Europe, Asia, Africa and North and South America. In 2010 the CTA Consortium completed a Design Study and started a three-year Preparatory Phase which leads to production readiness of CTA in 2014. In this paper we introduce the science goals and the concept of CTA, and provide an overview of the project. (C) 2013 Elsevier B.V. All rights reserved.
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| 2. |
- Actis, M., et al.
(författare)
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Design concepts for the Cherenkov Telescope Array CTA : an advanced facility for ground-based high-energy gamma-ray astronomy
- 2011
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Ingår i: Experimental astronomy. - : Springer. - 0922-6435 .- 1572-9508. ; 32:3, s. 193-316
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Tidskriftsartikel (refereegranskat)abstract
- Ground-based gamma-ray astronomy has had a major breakthrough with the impressive results obtained using systems of imaging atmospheric Cherenkov telescopes. Ground-based gamma-ray astronomy has a huge potential in astrophysics, particle physics and cosmology. CTA is an international initiative to build the next generation instrument, with a factor of 5-10 improvement in sensitivity in the 100 GeV-10 TeV range and the extension to energies well below 100 GeV and above 100 TeV. CTA will consist of two arrays (one in the north, one in the south) for full sky coverage and will be operated as open observatory. The design of CTA is based on currently available technology. This document reports on the status and presents the major design concepts of CTA.
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| 3. |
- Emile-Geay, J., et al.
(författare)
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Data Descriptor: A global multiproxy database for temperature reconstructions of the Common Era
- 2017
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Ingår i: Scientific Data. - : Springer Science and Business Media LLC. - 2052-4463. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- Reproducible climate reconstructions of the Common Era (1 CE to present) are key to placing industrial-era warming into the context of natural climatic variability. Here we present a community-sourced database of temperature-sensitive proxy records from the PAGES2k initiative. The database gathers 692 records from 648 locations, including all continental regions and major ocean basins. The records are from trees, ice, sediment, corals, speleothems, documentary evidence, and other archives. They range in length from 50 to 2000 years, with a median of 547 years, while temporal resolution ranges from biweekly to centennial. Nearly half of the proxy time series are significantly correlated with HadCRUT4.2 surface temperature over the period 1850-2014. Global temperature composites show a remarkable degree of coherence between high-and low-resolution archives, with broadly similar patterns across archive types, terrestrial versus marine locations, and screening criteria. The database is suited to investigations of global and regional temperature variability over the Common Era, and is shared in the Linked Paleo Data (LiPD) format, including serializations in Matlab, R and Python. Since the pioneering work of D'Arrigo and Jacoby1-3, as well as Mann et al. 4,5, temperature reconstructions of the Common Era have become a key component of climate assessments6-9. Such reconstructions depend strongly on the composition of the underlying network of climate proxies10, and it is therefore critical for the climate community to have access to a community-vetted, quality-controlled database of temperature-sensitive records stored in a self-describing format. The Past Global Changes (PAGES) 2k consortium, a self-organized, international group of experts, recently assembled such a database, and used it to reconstruct surface temperature over continental-scale regions11 (hereafter, ` PAGES2k-2013'). This data descriptor presents version 2.0.0 of the PAGES2k proxy temperature database (Data Citation 1). It augments the PAGES2k-2013 collection of terrestrial records with marine records assembled by the Ocean2k working group at centennial12 and annual13 time scales. In addition to these previously published data compilations, this version includes substantially more records, extensive new metadata, and validation. Furthermore, the selection criteria for records included in this version are applied more uniformly and transparently across regions, resulting in a more cohesive data product. This data descriptor describes the contents of the database, the criteria for inclusion, and quantifies the relation of each record with instrumental temperature. In addition, the paleotemperature time series are summarized as composites to highlight the most salient decadal-to centennial-scale behaviour of the dataset and check mutual consistency between paleoclimate archives. We provide extensive Matlab code to probe the database-processing, filtering and aggregating it in various ways to investigate temperature variability over the Common Era. The unique approach to data stewardship and code-sharing employed here is designed to enable an unprecedented scale of investigation of the temperature history of the Common Era, by the scientific community and citizen-scientists alike.
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| 4. |
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| 5. |
- Luterbacher, J., et al.
(författare)
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European summer temperatures since Roman times
- 2016
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 11:2
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Tidskriftsartikel (refereegranskat)abstract
- The spatial context is criticalwhen assessing present-day climate anomalies, attributing them to potential forcings and making statements regarding their frequency and severity in a long-term perspective. Recent international initiatives have expanded the number of high-quality proxy-records and developed new statistical reconstruction methods. These advances allow more rigorous regional past temperature reconstructions and, in turn, the possibility of evaluating climate models on policy-relevant, spatiotemporal scales. Here we provide a new proxy-based, annually-resolved, spatial reconstruction of the European summer (June-August) temperature fields back to 755 CE based on Bayesian hierarchical modelling (BHM), together with estimates of the European mean temperature variation since 138 BCE based on BHM and composite-plus-scaling (CPS). Our reconstructions compare well with independent instrumental and proxy-based temperature estimates, but suggest a larger amplitude in summer temperature variability than previously reported. Both CPS and BHM reconstructions indicate that the mean 20th century European summer temperature was not significantly different from some earlier centuries, including the 1st, 2nd, 8th and 10th centuries CE. The 1st century (in BHM also the 10th century) may even have been slightly warmer than the 20th century, but the difference is not statistically significant. Comparing each 50 yr period with the 1951-2000 period reveals a similar pattern. Recent summers, however, have been unusually warm in the context of the last two millennia and there are no 30 yr periods in either reconstruction that exceed the mean average European summer temperature of the last 3 decades (1986-2015 CE). A comparison with an ensemble of climate model simulations suggests that the reconstructed European summer temperature variability over the period 850-2000 CE reflects changes in both internal variability and external forcing on multi-decadal time-scales. For pan-European temperatures we find slightly better agreement between the reconstruction and the model simulations with high-end estimates for total solar irradiance. Temperature differences between the medieval period, the recent period and the Little Ice Age are larger in the reconstructions than the simulations. This may indicate inflated variability of the reconstructions, a lack of sensitivity and processes to changes in external forcing on the simulated European climate and/or an underestimation of internal variability on centennial and longer time scales.
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| 6. |
- Zhong, Cheng, et al.
(författare)
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Temporal Changes in Microbial Community Composition and Geochemistry in Flowback and Produced Water from the Duvernay Formation
- 2019
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Ingår i: ACS Earth and Space Chemistry. - : American Chemical Society (ACS). - 2472-3452. ; 3:6, s. 1047-1057
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Tidskriftsartikel (refereegranskat)abstract
- Microbial activity in flowback and produced water (FPW) may negatively influence shale oil and gas extraction. However, the impacts of using recycled produced water (RPW) for subsequent fracturing jobs are not well-understood. In this study, we compared time series of FPW samples from two horizontally fractured wells drilled into the Duvernay Formation in Alberta, Canada; well 1 used RPW in the makeup of the hydraulic fracturing fluid (HFF) whereas well 2 did not. 16S rRNA gene sequencing and live/dead cell enumeration were used to track microbial communities. Within 20 days of flowback, total dissolved solids in well 1 and well 2 increased from 5310 mg/L and 288 mg/L to over 150,000 mg/L, and FPW temperatures increased from 20 and 9 degrees C to 77 and 71 degrees C, respectively. Alkyl dimethyl benzyl ammonium chloride (biocide) in well 2 decreased from 25 mu g/L to below the detection limit of 0.5 mu g/L. Cellular biomass decreased from similar to 10(5) cells mL(-1) to less than the detection limit of 10(5) cells mL(-1) in both wells, and the community in the samples was initially diverse but rapidly shifted to become dominated by the sulfidogenic lineage Halanaerobium. Methanogens were detected at low relative abundance within archaea, with DNA concentrations in FPW after 20 days inadequate for sequencing. Comparing the two wells, the start time of Halanaerobium enrichment was considerably shortened in well 1 relative to well 2. Our results suggest that subsurface environmental parameters primarily drive the rapid enrichment of sulfidogenic and halotolerant bacteria and current recycling strategies can facilitate the growth of these bacteria, whereas biocide seems to be a less important factor in this shift.
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| 7. |
- Abram, Nerilie J., et al.
(författare)
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Early onset of industrial-era warming across the oceans and continents
- 2016
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 536:7617, s. 411-418
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Tidskriftsartikel (refereegranskat)abstract
- The evolution of industrial-era warming across the continents and oceans provides a context for future climate change and is important for determining climate sensitivity and the processes that control regional warming. Here we use post-ad 1500 palaeoclimate records to show that sustained industrial-era warming of the tropical oceans first developed during the mid-nineteenth century and was nearly synchronous with Northern Hemisphere continental warming. The early onset of sustained, significant warming in palaeoclimate records and model simulations suggests that greenhouse forcing of industrial-era warming commenced as early as the mid-nineteenth century and included an enhanced equatorial ocean response mechanism. The development of Southern Hemisphere warming is delayed in reconstructions, but this apparent delay is not reproduced in climate simulations. Our findings imply that instrumental records are too short to comprehensively assess anthropogenic climate change and that, in some regions, about 180 years of industrial-era warming has already caused surface temperatures to emerge above pre-industrial values, even when taking natural variability into account.
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| 8. |
- Bigler, Christian, et al.
(författare)
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Quantifying human-induced eutrophication in Swiss mountain lakes since AD 1800 using diatoms
- 2007
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Ingår i: The Holocene. - : SAGE Publications. - 0959-6836 .- 1477-0911. ; 17:8, s. 1141-1154
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Tidskriftsartikel (refereegranskat)abstract
- Sedimentary diatom assemblages from three lakes in the southeastern Swiss Alps were analysed at high temporal resolution since AD 1800. Altered land-use patterns, increasing population and exploitation through tourism are clearly reflected in annually laminated sediments of Lej da San Murezzan (Lake St Moritz) and Lej da Silvaplauna (Lake Silvaplana). Diatom assemblages originally dominated by Cyclotella taxa are replaced by taxa indicating higher total phosphorus (TP) concentrations, such as Asterionella formosa, Fragilaria crotonensis and Stephanodiscus parvus. In Lej da la Tscheppa, located well above the treeline in a catchment that was hardly exposed to human impact, Cyclotella comensis prevails throughout the entire sediment sequence. Quantitative estimates of past TP concentrations were inferred using a newly developed regional diatom-TP inference model based on 119 modern samples. In Lej da la Tscheppa diatoms imply stable, low TP concentrations (~10 µg/l), which can be considered as natural background concentration. Elevated TP levels are inferred for Lej da San Murezzan (max. 60 µg/l) since AD 1910 and for Lej da Silvaplauna (max. 40 µg/l) since AD 1950, corroborated by changes in sedimentary biogenic silica concentration and organic carbon content. Since ~AD 1970 improved waste water management led to a considerable reduction in TP loading in Lej da Silvaplauna and Lej da San Murezzan.
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| 9. |
- Kaufman, DS, et al.
(författare)
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Technical note: Open-paleo-data implementation pilot-The PAGES 2k special issue
- 2018
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Ingår i: Climate of the Past. - 1814-9324 .- 1814-9332. ; 14, s. 593-600
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Tidskriftsartikel (refereegranskat)abstract
- Data stewardship is an essential element of the publication process. Knowing how to enact data polices that are described only in general terms can be difficult, however. Examples are needed to model the implementation of open-data polices in actual studies. Here we explain the procedure used to attain a high and consistent level of data stewardship across a special issue of the journal Climate of the Past. We discuss the challenges related to (1) determining which data are essential for public archival, (2) using data generated by others, and (3) understanding data citations. We anticipate that open-data sharing in paleo sciences will accelerate as the advantages become more evident and as practices that reduce data loss become the accepted convention.
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| 10. |
- Turney, C. S. M., et al.
(författare)
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Introduction to the special issue "Climate of the past 2000 years: regional and trans-regional syntheses"
- 2019
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 15:2, s. 611-615
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Tidskriftsartikel (refereegranskat)abstract
- This PAGES (Past Global Changes) 2k (climate of the past 2000 years working group) special issue of Climate of the Past brings together the latest understanding of regional change and impacts from PAGES 2k groups across a range of proxies and regions. The special issue has emerged from a need to determine the magnitude and rate of change of regional and global climate beyond the timescales accessible within the observational record. This knowledge also plays an important role in attribution studies and is fundamental to understanding the mechanisms and environmental and societal impacts of recent climate change. The scientific studies in the special issue reflect the urgent need to better understand regional differences from a truly global view around the PAGES themes of "Climate Variability, Modes and Mechanisms", "Methods and Uncertainties", and "Proxy and Model Understanding".
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