1,720,967 research outputs found
The aerosols, radiation and clouds in Southern Africa field campaign in Namibia: overview, illustrative observations, and way forward
Get PDFThe Aerosol, Radiation and Clouds in southern Africa (AEROCLO-sA) project investigates the role of aerosols on the regional climate of southern Africa. This is a unique environment where natural and anthropogenic aerosols and a semipermanent and widespread stratocumulus (Sc) cloud deck are found. The project aims to understand the dynamical, chemical, and radiative processes involved in aerosol–cloud–radiation interactions over land and ocean and under various meteorological conditions. The AEROCLO-sA field campaign was conducted in August and September of 2017 over Namibia. An aircraft equipped with active and passive remote sensors and aerosol in situ probes performed a total of 30 research flight hours. In parallel, a ground-based mobile station with state-of-the-art in situ aerosol probes and remote sensing instrumentation was implemented over coastal Namibia, and complemented by ground-based and balloonborne observations of the dynamical, thermodynamical, and physical properties of the lower troposphere. The focus laid on mineral dust emitted from salty pans and ephemeral riverbeds in northern Namibia, the advection of biomass-burning aerosol plumes from Angola subsequently transported over the Atlantic Ocean, and aerosols in the marine boundary layer at the ocean–atmosphere interface. This article presents an overview of the AEROCLO-sA field campaign with results from the airborne and surface measurements. These observations provide new knowledge of the interactions of aerosols and radiation in cloudy and clear skies in connection with the atmospheric dynamics over southern Africa. They will foster new advanced climate simulations and enhance the capability of spaceborne sensors, ultimately allowing a better prediction of future climate and weather in southern Afric
Three years of measurements of light-absorbing aerosols over coastal Namibia: seasonality, origin, and transport
Get PDFContinuous measurements between July 2012 and December 2015 at the Henties Bay Aerosol Observatory (HBAO; 22∘ S, 14∘05′ E), Namibia, show that, during the austral wintertime, transport of light-absorbing black carbon aerosols occurs at low level into the marine boundary layer. The average of daily concentrations of equivalent black carbon (eBC) over the whole sampling period is 53 (±55) ng m−3. Peak values above 200 ng m−3 and up to 800 ng m−3 occur seasonally from May to August, ahead of the dry season peak of biomass burning in southern Africa (August to October). Analysis of 3-day air mass back-trajectories show that air masses from the South Atlantic Ocean south of Henties Bay are generally cleaner than air having originated over the ocean north of Henties Bay, influenced by the outflow of the major biomass burning plume, and from the continent, where wildfires occur. Additional episodic peak concentrations, even for oceanic transport, indicate that pollution from distant sources in South Africa and maritime traffic along the Atlantic ship tracks could be important. While we expect the direct radiative effect to be negligible, the indirect effect on the microphysical properties of the stratocumulus clouds and the deposition to the ocean could be significant and deserve further investigation, specifically ahead of the dry seaso
Characteristics and transport of atmospheric aerosols over the Namibian coast
Get PDFPhD (Geography and Environmental Management), North-West University, Potchefstroom CampusIt is well understood that on various scales in the atmosphere, the transport, dispersion, accumulation, transformation and deposition of aerosols is driven by atmospheric dynamics, meteorological conditions and topographical controls. This thesis presents the results of a series of inter-disciplinary research endeavours in environmental and atmospheric sciences to describe the spatial- and temporal variability in vertical atmospheric structures, transport pathways, and aerosol character over the Namibian coast. The unique topography, atmospheric conditions, variety of aerosol sources, and the presence of a semi-permanent stratocumulus cloud deck, make the Namibian coast of particular interest for this study and this region is a type of natural laboratory for studying the variability in these conditions. Recent international research efforts in the region include the Observations of aerosol and cloud interactions (Nasa-ORACLES: Zuidema et al., 2016) and the Aerosols, Clouds and Radiation in southern Africa (AEROCLO-sA: Formenti et al., 2019) campaigns. For the aforementioned reasons, the ground-based, Henties Bay Aerosol Observatory (HBAO; 22.090619°S, 14.272424°E), Namibia, makes in situ measurements of various physical and chemical properties of aerosols. These measurements within the Namibian boundary layer (BL) include black carbon (BC) intermittently from July 2012 to December 2015, and filter sampling of PM10 aerosols from February 2016 to December 2017 (over 26 sampling weeks). These filters were analysed for element- and ion-concentrations. Additionally, publicly available datasets were used, such as the NOAA HYSPLIT kinematic back-trajectory model, radiosonde data, remote-sensed satellite data from MODIS, CALIPSO and COSMIC missions, synoptic charts, reanalysis meteorological datasets, and statistical- and mathematical models. Boundary layer height (BLH), characterised by the bulk Richardson number, at Walvis Bay, were radiosondes were released was linked to cloud- and surface cover, surface heating effects, and easterly wind components. The surface of MG across the region of interest was largely affected by changes in atmospheric moisture and cloud, and was not consistent with BLH as defined by the bulk Richardson number. Low-level inversions, identified by GPS-RO, were lowest, deepest and strongest in the spring. Their character was linked to surface-radiation interactions with cold sea surfaces, warm arid landscapes and low-level clouds in the region, and macroscale circulation, such as the southeast Atlantic and continental high-pressure systems. The effects of diurnal variability in surface temperatures extended deep into the atmosphere with stability peaking just before dawn. The character of low-level inversions along the coast also indicated the presence of the night-time Benguela jet stream. The geographical variability and springtime maximums coincided with maximum closed cloud cover over the SEA Ocean and biomass burning aerosol (BBA) plumes over the region. The character of elevated inversions was also linked to macroscale circulation, as well as the spatial and temporal distribution of radiation-absorbing aerosols emitted by biomass burning. The transport pathways to the site, conceptualised with the use of synoptic charts and trajectory analyses, helped to identify several major transport pathways to the
aerosol observatory, from marine and continental atmospheres or recirculated locally. An early peak in equivalent black carbon (eBC) in comparison to literature and satellite measurements were explained by the influence of localised low-pressure systems that either enhance (July) or inhibit transport (September) into the Namibian BL. In addition, lower eBC in the BL in September may be linked to increased stability when co-occurring inversions were at a maximum for the year. In addition to the biomass burning source, five major aerosol source types were identified from the apportionment by comparisons of mass ratios to known literature values and positive matrix factorisation (PMF). These sources are sea salt (component contributes 74.7 ± 1.9% of the total mass, characterised by Na+, Cl-, Mg2+, K+, Ca2+ and SO42-), mineral dust (15.7 ± 1.4%, Si, Al, Fe, Ti, Ca2+, Mn, P, F- and V), ammonium neutralised (6.1 ± 0.7%, SO42-, NH4+, MSA, oxalate, and nitrate), fugitive dust (2.6 ± 0.2%, V, Cd, Pb, Nd and Sr) and industry (0.9 ± 0.7%, As, Zn, Cu, Ni and Sr). High fluoride concentrations (25 μg m-3) could pose a serious health problem to the affected populations. Back-trajectory analyses showed how aerosols were circulated locally and transported over great distances from the ocean and subcontinent. Even though the HBAO is set in a remote environment, the transport and contribution of aerosols generated by both natural and anthropogenic processes mean that the site cannot be considered as pristine. The combined interdisciplinary methods used in this study, have proven useful in investigating the influence of vertical structures in the atmosphere, and the local- and long-range transport of air masses on the aerosol character and load at HBAO.Doctora
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
NACA conference 2023 – Collaborating for clean air: Confronting climate change and air quality together
No full textDispelling the Myths Behind First-author Citation Counts
Get PDFWe 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
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