1,720,962 research outputs found
The evolution of the Polar-AOD network: towards a comprehensive repository supporting efforts for integrated polar observing systems
No full textAtmospheric aerosols play a crucial role in Earth's atmospheric environment and are among its most variable components. In polar regions, aerosols originate from both natural and anthropogenic sources. In the Arctic, the majority of the aerosol mass consists of oceanic sea-salt, mineral dust, non-sea-salt sulphate, and products of biomass burning (Tomasi et al. 2015). In contrast, anthropogenic aerosols are dominated by black carbon (BC) and nitrate, which are signatures of traffic and industrial emissions (Quinn et al. 2007). Polar aerosols can have significant regional effects by interacting with incoming solar radiation and by altering the albedo of the surface-atmosphere system (IPCC 2023). To address and study these effects, the Polar-AOD project was proposed for the first time in 1999 by Claudio Tomasi from the National Research Council of Italy. This initiative aims to characterize the means, variability, and trends of aerosol properties in polar regions. Its primary goal is to connect observational stations measuring aerosol properties along the atmospheric vertical column. These observations provide critical data to quantify aerosol physical and radiative properties at high latitudes, including seasonal background concentrations derived from aerosol optical depth (AOD) measurements, spectral characterizations, and the influence of natural and anthropogenic processes on the radiative balance of the surface and atmosphere. This project fosters collaboration among scientists in the field of photometry at both poles. It also incorporates the stellar and lunar photometry data, which help to address historical gaps in AOD climatologies during the polar night. By filling these gaps, the Polar-AOD project contributes to a comprehensive understanding of aerosol behavior and its impacts on the polar regions. To support this effort, a new web platform has been recently developed to store and share data and metadata from photometric measurements, forming a polar AOD archive. This archive, managed by CNR through GeoNetwork, enables the organization and search of spatially referenced resources while allowing each scientific group to manage its own data, choosing to share metadata only or both data and metadata for specific sites or campaigns within the Polar-AOD network. The new data portal will be presented, along with the maps of the stations and instruments, and the Polar-AOD metadata catalogue
Haloacetic Acids as Contaminants of Emerging Concern in Arctic Aerosol
No full textHaloacetic acids are concerning emerging contaminants defined mainly as disinfection byproducts. Extensively studied in water environments, they are still poorly investigated in atmospheric aerosols and only in midlatitude anthropized countries. To our knowledge, this is the first study reporting the evidence of 12 brominated, chlorinated, and iodinated-acetic acids in the Arctic particulate matter. This paper had three main goals: 1) to evaluate the occurrence of the 12 haloacetic acids in the Arctic atmospheric aerosol, 2) to identify their possible sources, and 3) to understand their transport patterns. Samples were collected in Ny-Ålesund (Svalbard Islands, Norwegian Arctic) during an entire sampling year, starting from February 2022 to March 2023. Trace concentrations of these species were determined using a high pressure anion exchange coupled with a triple quadrupole, defining the monohaloacetic acids as the most ubiquitous compounds. In particular, the most abundant species was monochloroacetic acid with a mean concentration of 35 ± 32 pg m–3. The statistical approach was applied to accomplish our goals: it highlighted the long-range transports and therefore anthropogenic input as the most important contribution for the investigated species. Considering their photosensitivity, future studies will be addressed to investigate the photochemical reactions of haloacetic acids in the complex polar atmosphere
Surface radiation budget data in a bipolar perspective: observations, comparison and exploiting for products
No full textClouds modulate the net radiative flux interacting with both shortwave and longwave radiation, but the uncertainties regarding their effect in polar regions are especially high, because ground observations are lacking and evaluation through satellites is made difficult by the high surface reflectance. In this work, the radiative regimes and sky conditions for five different stations, two in the Arctic (Ny-Ålesund, 78.92°N, 11.93°E, Barrow, 71.32°N, 156.61° W) and four in Antarctica (Neumayer, 70.68°S, 8.27°W; Syowa, 69.01°S, 39.58°E; South Pole, 90°S, 0°E ; DomeC, 75.01°S, 123.33°E) will be presented, considering the decade between 2010 and 2020. Measurements of broadband shortwave and longwave radiation components (both downwelling and upwelling) are collected within the frame of the Baseline Surface Radiation Network (BSRN) (Driemel et al. 2018). Observations, together with identification of the clear sky and overcast conditions will be compared with ERA5 reanalysis (Herschbach et al., 2023). Furthermore, the identified conditions based on estimated cloud fraction will serve as labels for a machine learning classification task, leveraging algorithms such as Random Forest and Long Short-Term Memory (LSTM) networks (i.e. Zeng et al., 2021; Sedlar et al., 2021). These models incorporate features including global and diffuse shortwave radiation, downward longwave radiation, solar zenith angle, surface air temperature, relative humidity, and the ratio of water vapor pressure to surface temperature. The Random Forest model will also compute feature importance, identifying the most influential variables in predicting sky conditions and providing insights into the relationships between these meteorological factors
Surface Broadband Radiation Data from a Bipolar Perspective: Assessing Climate Change Through Machine Learning
Full text linkClouds modulate the net radiative flux that interacts with both shortwave (SW) and longwave (LW) radiation, but the uncertainties regarding their effect in polar regions are especially high because ground observations are lacking and evaluation through satellites is made difficult by high surface reflectance. In this work, sky conditions for six different polar stations, two in the Arctic (Ny-Ålesund and Utqiagvik [formerly Barrow]) and four in Antarctica (Neumayer, Syowa, South Pole, and Dome C) will be presented, considering the decade between 2010 and 2020. Measurements of broadband SW and LW radiation components (both downwelling and upwelling) are collected within the frame of the Baseline Surface Radiation Network (BSRN). Sky conditions—categorized as clear sky, cloudy, or overcast—were determined using cloud fraction estimates obtained through the RADFLUX method, which integrates shortwave (SW) and longwave (LW) radiative fluxes. RADFLUX was applied with daily fitting for all BSRN stations, producing two cloud fraction values: one derived from shortwave downward (SWD) measurements and the other from longwave downward (LWD) measurements. The variation in cloud fraction used to classify conditions from clear sky to overcast appeared consistent and reasonable when compared to seasonal changes in shortwave downward (SWD) and diffuse radiation (DIF), as well as longwave downward (LWD) and longwave upward (LWU) fluxes. These classifications served as labels for a machine learning-based classification task. Three algorithms were evaluated: Random Forest, K-Nearest Neighbors (KNN), and XGBoost. Input features include downward LW radiation, solar zenith angle, surface air temperature (Ta
), relative humidity, and the ratio of water vapor pressure to Ta
. Among these models, XGBoost achieved the highest balanced accuracy, with the best scores of 0.78 at Ny-Ålesund (Arctic) and 0.78 at Syowa (Antarctica). The evaluation employed a leave-one-year-out approach to ensure robust temporal validation. Finally, the results from cross-station models highlighted the need for deeper investigation, particularly through clustering stations with similar environmental and climatic characteristics to improve generalization and transferability across locations. Additionally, the use of feature normalization strategies proved effective in reducing inter-station variability and promoting more stable model performance across diverse settings
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Investigating the Presence of Biomass Burning Events at Ny-Ålesund: Optical and Chemical Insights from Summer-Fall 2019
No full textSummer 2019 is remembered as one of the most intense biomass burning (BB) seasons on record for the Northern Hemisphere. During the MOSAiC expedition, a smoke-dominated layer was identified in the upper
troposphere over the North Pole region. The origin of this layer remains unclear, and no evidence has been
found to indicate the intrusion of such particles into the Arctic Boundary Layer. The main aim of this work
was to evaluate if biomass burning events in the summer 2019 were detectable at Gruvebadet Atmospheric
Laboratory, close to Ny-Ålesund (Svalbard Islands) during the second half of 2019. This paper proposes
an innovative approach to discriminate biomass burning events based on optical measurements combined
with chemical analysis and air mass back-trajectories. Monthly background values of optical coefficients
were defined using multi-annual (2018–2021) statistics and twelve possible events were identified. Source
apportionment through positive matrix factorization (PMF) identified that the biomass burning factor by PMF
accounted for only 2% of the total investigated concentration. The specific biomass burning tracers such as
levoglucosan and phenolic compounds were compared with optical measurements and with the PMF results.
Air mass trajectory analysis revealed that the early summer fires detected at Ny-Ålesund originated mainly
from North America, as also confirmed by the presence of BB factor of PMF, levoglucosan and also vanillic
species (softwood combustion tracers). In contrast, the chemical composition and air masses analysis of the
highest peak detected in early December suggested residential heating as plausible source, further amplified
by the onset of the harsh winter season and the expansion of the polar vortex towards mid-latitudes
Variations on the Author
Full text link“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
Full text linkWe 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
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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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