1,720,965 research outputs found
Day-by-day modelling of the ionospheric F2-layer for year 2002
No full textThe thermosphere–ionosphere–mesosphere-electrodynamics general circulation model (TIME-GCM) has been run for the year 2002. Its version 1.2 features include day-by-day input of solar irradiance, geomagnetic energy input parameterized by the 3-h Kp index, and global lower boundary conditions from the National Centres for Environmental Prediction (NCEP) data. In addition, it includes tidal forcing from the global-scale wave model (GSWM) and parameterized gravity waves from below. The computed day-by-day values of noon peak electron density NmF2 agree well with ionosonde data for five northern sites and two southern mid-latitude sites, and closely follow the day-by-day modelled concentration ratio of atomic oxygen to molecular nitrogen. Seasonal and hemispheric patterns appear in the model with some, though not full, success. The model's day-to-day patterns show an impressive degree of variability, with simulations of total variability both above and below those observed.<br/
Modelling F2-layer seasonal trends and day-to-day variability driven by coupling with the lower atmosphere
No full textThis paper presents results from the TIME-GCM-CCM3 thermosphere–ionosphere–lower atmosphere flux-coupled model, and investigates how well the model simulates known F2-layer day/night and seasonal behaviour and patterns of day-to-day variability at seven ionosonde stations. Of the many possible contributors to F2-layer variability, the present work includes only the influence of ‘meteorological’ disturbances transmitted from lower levels in the atmosphere, solar and geomagnetic conditions being held at constant levels throughout a model year.In comparison to ionosonde data, TIME-GCM-CCM3 models the peak electron density (NmF2) quite well, except for overemphasizing the daytime summer/winter anomaly in both hemispheres and seriously underestimating night NmF2 in summer. The peak height hmF2 is satisfactorily modelled by day, except that the model does not reproduce its observed semiannual variation. Nighttime values of hmF2 are much too low, thus causing low model values of night NmF2. Comparison of the variations of NmF2 and the neutral [O/N2] ratio supports the idea that both annual and semiannual variations of F2-layer electron density are largely caused by changes of neutral composition, which in turn are driven by the global thermospheric circulation.Finally, the paper describes and discusses the characteristics of the F2-layer response to the imposed ‘meteorological’ disturbances. The ionospheric response is evaluated as the standard deviations of five ionospheric parameters for each station within 11-day blocks of data. At any one station, the patterns of variability show some coherence between different parameters, such as peak electron density and the neutral atomic/molecular ratio. Coherence between stations is found only between the closest pairs, some 2500 km apart, which is presumably related to the scale size of the ‘meteorological’ disturbances. The F2-layer day-to-day variability appears to be related more to variations in winds than to variations of thermospheric composition
A stable auroral red arc over Europe
No full textUsing a new all-sky-imaging system, M Mendillo, C Barbieri, J Baumgardner, J Wroten, G Cremonese and G Umbriaco observed two distinctive types of aurora over London and western Europe on the night of 26-27 September 2011, including the first ground-based image of a stable auroral red arc over Europe. 2012 Royal Astronomical Society
Imaging Space Weather Over Europe from a Single Site
No full textWe have recently installed a low-light-level, all-sky-imager (ASI) at the astronomical observatory in Asiago, Italy (45.8 N, 11.5 E, 41 N geomagnetic). The field-of-view for such a system can yield reliable observations from zenith down to about five degrees elevation angle. Atmospheric emissions arise from different altitudes and thus the spatial region observed by an ASI depends on the specific wavelength (and process) involved. For 6300 A emissions from atomic oxygen, diffuse aurora occur at ~200 km, ambient airglow at ~300 km and so-called Stable Auroral Red (SAR) arcs at ~400 km. From the Asiago site, the FOV at 400 km spans latitudes extending from southern Scandanavia to Northern Africa. For a magnetic latitude of 50 N, longitudes observed to the north extend from Ireland to Belarus. For a magnetic latitude of 30 N, longitudes to the south can be observed from Spain to Turkey. The SAR arc that occurred during the geomagnetic storm 26-27 September 2011 was, we think, the first-ever such event imaged from the ground in Europe. The SAR arc’s location throughout the night maps to the inner magnetosphere where the plasmapause and inner edge of the ring current coincide. The spatial-temporal positions of these features determine the lowest latitudes of magnetosphere-ionospheric energy input during space weather events. We show that an all-sky-imager can thus be used to provide real-time information of this boundary over most of Europe—and thus the low-latitude limit of the radiowave scintillations associated with SAR arcs. Moreover, such information can be used for retrospective validations of global models that predict the latitude extent of space weather effects
Imaging Space Weather Over Europe from a Single Site
No full textWe have recently installed a low-light-level, all-sky-imager (ASI) at the astronomical observatory in Asiago, Italy (45.8 N, 11.5 E, 41 N geomagnetic). The field-of-view for such a system can yield reliable observations from zenith down to about five degrees elevation angle. Atmospheric emissions arise from different altitudes and thus the spatial region observed by an ASI depends on the specific wavelength (and process) involved. For 6300 A emissions from atomic oxygen, diffuse aurora occur at ~200 km, ambient airglow at ~300 km and so-called Stable Auroral Red (SAR) arcs at ~400 km. From the Asiago site, the FOV at 400 km spans latitudes extending from southern Scandanavia to Northern Africa. For a magnetic latitude of 50 N, longitudes observed to the north extend from Ireland to Belarus. For a magnetic latitude of 30 N, longitudes to the south can be observed from Spain to Turkey. The SAR arc that occurred during the geomagnetic storm 26-27 September 2011 was, we think, the first-ever such event imaged from the ground in Europe. The SAR arc’s location throughout the night maps to the inner magnetosphere where the plasmapause and inner edge of the ring current coincide. The spatial-temporal positions of these features determine the lowest latitudes of magnetosphere-ionospheric energy input during space weather events. We show that an all-sky-imager can thus be used to provide real-time information of this boundary over most of Europe—and thus the low-latitude limit of the radiowave scintillations associated with SAR arcs. Moreover, such information can be used for retrospective validations of global models that predict the latitude extent of space weather effects
First Conjugate Observations of Medium-Scale Traveling Ionospheric Disturbances (MSTIDs) in the Europe-Africa Longitude Sector
Full text linkAll-sky imagers located in Asiago, Italy (45.87oN, 11.53oE; 40.7o magnetic latitude) and Sutherland, South Africa (32.37oS, 20.81oE; −40.7o magnetic latitude) are used to study magnetically conjugate medium scale traveling ionospheric disturbances (MSTIDs). We present initial results from the first year of joint Asiago-Sutherland data sets from July 2016 to June 2017. The 630.0-nm airglow perturbations showing different kinds of waves were frequently observed. Some of these wave events resemble MSTIDs propagating south-westward in Asiago, typical direction observed at other longitude sectors in the northern hemisphere. They are mostly observed as single bands propagating through the field of view of the all-sky imagers. We select and analyze five cases of magnetically conjugate bands associated with MSTIDs. The bands observed at Sutherland move mainly westward, noticeably different from the north-west direction of propagation of MSTIDs observed in the southern hemisphere. We compare the MSTIDs propagation speeds and find that three cases show larger values at Sutherland. When we compare the zonal speeds all the cases show larger values at Sutherland. On average, the propagation speed at Sutherland is 20% larger and the zonal speed is ~35% larger. The westward motion at Sutherland is explained by taking onto account how its magnetic declination (~24oW) affects the orientation of the bands. The larger speed at Sutherland is due to the weaker Earth's magnetic field in the southern hemisphere and the particular configuration of the magnetic field lines in this longitude sector.All-sky imagers located in Asiago, Italy (45.87 o N, 11.53 o E; 40.7 o magnetic latitude) and Sutherland, South Africa (32.37 o S, 20.81 o E; −40.7 o magnetic latitude) are used to study magnetically conjugate medium scale traveling ionospheric disturbances (MSTIDs). We present initial results from the first year of joint Asiago-Sutherland data sets from July 2016 to June 2017. The 630.0-nm airglow perturbations showing different kinds of waves were frequently observed. Some of these wave events resemble MSTIDs propagating south-westward in Asiago, typical direction observed at other longitude sectors in the northern hemisphere. They are mostly observed as single bands propagating through the field of view of the all-sky imagers. We select and analyze five cases of magnetically conjugate bands associated with MSTIDs. The bands observed at Sutherland move mainly westward, noticeably different from the north-west direction of propagation of MSTIDs observed in the southern hemisphere. We compare the MSTIDs propagation speeds and find that three cases show larger values at Sutherland. When we compare the zonal speeds all the cases show larger values at Sutherland. On average, the propagation speed at Sutherland is 20% larger and the zonal speed is ~35% larger. The westward motion at Sutherland is explained by taking onto account how its magnetic declination (~24 o W) affects the orientation of the bands. The larger speed at Sutherland is due to the weaker Earth's magnetic field in the southern hemisphere and the particular configuration of the magnetic field lines in this longitude sector
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
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
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