323,208 research outputs found
Data used to produce figures in the manuscript ‘Maximizing Ozone Signals Among Chemical, Meteorological, and Climatological Variability’ by Brown-Steiner et al. (2018)
No full textData used to produce figures in the manuscript ‘Maximizing Ozone Signals Among Chemical, Meteorological, and Climatological Variability’ by Brown-Steiner, B.; Selin, N. E.; Prinn, R. G.; Monier, E.; Tilmes, S.; Emmons, L.; Garcia-Menendez, F
Sensitivity of the Methane Lifetime to Sulfate Geoengineering: Results from the Geoengineering Model Intercomparison Project (GeoMIP)
No full textSulfate geoengineering, made by sustained injection of SO2 in the tropical lower stratosphere, may impact the abundance of tropospheric methane through several photochemical mechanisms affecting the tropospheric OH abundance and hence the methane lifetime. Geoengineered sulfate aerosols in the stratosphere are responsible of important radiative and chemical effects: (a) solar radiation scattering increases the planetary albedo and cools the surface, with a tropospheric water vapor decrease as a response to this cooling: less OH. (b) The tropospheric UV budget is upset by the additional aerosol scattering and stratospheric ozone changes: the net effect is meridionally not uniform, with a net decrease in the tropics, thus producing less tropospheric O(1D): less OH. (c) The extratropical downwelling motion from the lower stratosphere tends to increase the sulfate aerosol surface area density available for heterogeneous chemical reactions in the mid-upper troposphere, thus reducing the amount of NOx and tropospheric O3 production: less OH. (d) The tropical lower stratosphere is warmed by solar and planetary radiation absorption by the aerosols. The heating rates perturbation are strongly latitude dependent, producing a significant change of the pole-to-equator temperature gradient and mean zonal wind distribution, with a net increase of tropical upwelling. A stronger meridional component of the Brewer-Dobson circulation may affect the abundance of mid-upper tropospheric sulfate aerosols, NOy, and O3 (all possibly affecting the budget of tropospheric OH), as well as CH4 transport directly. Three climate-chemistry coupled models are used here to explore the above radiative, chemical and dynamical mechanisms affecting the methane lifetime (ULAQ-CCM, CCSM4, GEOSCCM). First results show that the CH4 lifetime may become significantly longer (Fig.1) with a sustained injection of 2.5 Tg-S/yr started in year 2020 (exp. G4), which implies an increase of tropospheric CH4 (Fig. 2) and a positive indirect RF of sulfate geoengineering due to CH4 changes, of the order of 10% the aerosols direct forcing, but with opposite sign
Data used to produce figures in the manuscript 'Evaluating Simplified Chemical Mechanisms within Present-Day Simulations of CESM Version 1.2 CAM-chem (CAM4): MOZART-4 vs. Reduced Hydrocarbon vs. Super-Fast Chemistry' by Brown-Steiner et al. (2018)
No full textData used to produce figures in the manuscript Evaluating Simplified Chemical Mechanisms within Present-Day Simulations of CESM Version 1.2 CAM-chem (CAM4): MOZART-4 vs. Reduced Hydrocarbon vs. Super-Fast Chemistry by Brown-Steiner, B.; Selin, N. E.; Prinn, R.; Tilmes, S.; Emmons, L.; Lamarque, J.-F.; and Cameron-Smith, P
Chemical ozone loss in the Arctic winter 1991–1992
No full textChemical ozone loss in winter 1991–1992 is recalculated based on observations of the HALOE satellite instrument, Version 19, ER-2 aircraft measurements and balloon data. HALOE satellite observations are shown to be reliable in the lower stratosphere below 400 K, at altitudes where the measurements are most likely disturbed by the enhanced sulfate aerosol loading, as a result of the Mt.~Pinatubo eruption in June 1991. Significant chemical ozone loss (13–17 DU) is observed below 380 K from Kiruna balloon observations and HALOE satellite data between December 1991 and March 1992. For the two winters after the Mt. Pinatubo eruption, HALOE satellite observations show a stronger extent of chemical ozone loss towards lower altitudes compared to other Arctic winters between 1991 and 2003. In spite of already occurring deactivation of chlorine in March 1992, MIPAS-B and LPMA balloon observations indicate that chlorine was still activated at lower altitudes, consistent with observed chemical ozone loss occurring between February and March and April. Large chemical ozone loss of more than 70 DU in the Arctic winter 1991–1992 as calculated in earlier studies is corroborated here
Diffusive author(s), cohesive author: Analysis of S/N (1994)
No full textThis study indicates the ways in which various aspects of the author(s) are brought forth in Dumb type’s performance art, the S/N production. Previous research has suggested a non-hierarchical organization of Dumb type and the absence of a “privileged author” in Dumb type’s collaborative work, S/N. However, the results that I have investigated from member’s interviews on the creative process of S/N along with my analysis of the recorded images of S/N, indicate a different aspect of the author(s). First, S/N was created through, so to speak, the collective ideas of the members of Dumb type. Further, S/N has at least nine quotations from previous performances, installations, and printed writings, besides the work-in-progress technique. Explicating one of the “author functions” as given by Michel Foucault, each text has plural subjects of the author. However, it has been revealed from members’ interviews that Teiji Furuhashi had a decision-making role in selecting the members’ ideas within the performance. Since then, S/N has had plural subjects of creation; however, Furuhashi is one of the subjects of creation along with the “privileged author.” S/N has plural authors (diffusive authors) yet at the same time, it has a “privileged author,” Teiji Furuhashi (cohesive author)
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
A new Geoengineering Model Intercomparison Project (GeoMIP) experiment designed for climate and chemistry models
No full textA new Geoengineering Model Intercomparison Project (GeoMIP) experiment “G4 specified
stratospheric aerosols” (short name: G4SSA) is proposed to investigate the impact of stratospheric
aerosol geoengineering on atmospheric composition, climate, and the environment. In contrast
to the earlier G4 GeoMIP experiment, which requires an emission of SO2 into the model, a
prescribed aerosol forcing file is provided to the community, to be consistently 5 applied to future
model experiments between 2020 and 2100. This stratospheric aerosol distribution, with a total burden
of about 2 Tg S has been derived using the ECHAM5-HAM microphysical model, based on a
continuous annual tropical emission of 8 Tg SO2. A ramp-up of geoengineering in 2020 and a rampdown
in 2070 over a period of two years are included in the distribution, while a background aerosol
10 burden should be used for the last 3 decades of the experiment. The performance of this experiment
using climate and chemistry models in a multi-model comparison framework will allow us to better
understand the significance of the impact of geoengineering and the abrupt termination after 50 years
on climate and composition of the atmosphere in a changing environment. The zonal and monthly
mean stratospheric aerosol input dataset is available at https://www2.acd.ucar.edu/gcm/geomip-g4-
15 specified-stratospheric-aerosol-data-set
Sensitivity of Methane Lifetime and Transport to Sulfate Geoengineering
No full textSulfate geoengineering, made by sustained injection of SO2 in the tropical lower stratosphere, may impact the abundance of tropospheric methane through several photochemical mechanisms affecting the tropospheric OH abundance and hence the methane lifetime. Changes of the stratospheric Brewer-Dobson circulation also play a role in the upper tropospheric CH4 transport. Three mechanisms lead to lower OH concentrations and a longer CH4 lifetime: (a) solar radiation scattering increases the planetary albedo and cools the surface, with a tropospheric water vapor decrease as a response to this cooling. (b) The tropospheric UV budget is upset by the additional aerosol scattering and stratospheric ozone changes: the net effect is meridionally not uniform, with a net decrease in the tropics, thus producing less tropospheric O(1D). (c) The extra-tropical downwelling motion from the lower stratosphere tends to increase the sulfate aerosol surface area density available for heterogeneous chemical reactions in the mid-upper troposphere, thus reducing the amount of NOx and tropospheric O3 production. On the other hand, the tropical lower stratosphere is warmed by solar and planetary radiation absorption by the aerosols. The heating rates perturbation are strongly latitude dependent, producing a significant change of the pole-to-equator temperature gradient and mean zonal wind distribution, with a net increase of tropical upwelling. A stronger meridional component of the Brewer-Dobson circulation increases the extra-tropical stratosphere to troposphere transport of CH4 poorer air, resulting in less CH4 transported in the UTLS. The net effect on tropospheric OH may be positive or negative depending on the net result of different superimposed species perturbations in the UTLS, i.e. CH4 (negative), NOy and O3 (positive). Three climate-chemistry coupled models are used here to explore the above radiative, chemical and dynamical mechanisms affecting the methane lifetime (ULAQ-CCM, GEOSCCM, CCSM-CAM4). First results show that the CH4 lifetime may become significantly longer (by about 10%) with a sustained injection of 2.5 Tg-S/yr started in year 2020, which implies an increase of tropospheric CH4 (200 ppbv) and a positive indirect radiative forcing of sulfate geoengineering due to CH4 changes (+0.1 W/m2 in the 2045)
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