1,720,962 research outputs found
Bubble-like Ionospheric Irregularities observed in the United States during the 26 August 2018 Geomagnetic Storm
No full textMultiantenna-Based Data Filling Method for Retrieving Electron Density Profiles From GNSS Radio Occultation Data
No full textRetrieval of ionospheric electron density below low Earth orbit (LEO) altitude using global navigation satellite system radio occultation (RO) sounding requires total electron content (TEC) calibration by subtracting TEC on the non-occultation side from that on the occultation side. However, this calibration is not applicable to RO missions, where the occultation antennas cannot observe non-occultation side TEC. This article proposes a methodology for retrieving ionospheric electron density through multiantenna-based data filling. The non-occultation side TEC observed by using a precise orbit determination (POD) antenna data is connected to the occultation side TEC observed by an occultation antenna, enabling the application of the calibration technique. The methodology involves modeling TEC in the remaining gap between the data from POD and occultation antennas by utilizing the Epstein function with a varying scale height. The interior-point method is used to determine the optimal parameters for the function that best fits the observations. The proposed method is validated by applying it to Korean multipurpose satellite-5 (KOMPSAT-5) data and comparing the electron densities retrieved from KOMPSAT-5 data with collocated ionosonde observations. The results demonstrate that the electron density values retrieved by the proposed algorithm are in good agreement with those obtained from ionosonde measurements.
Do Solar Eclipses Generate Propagating Ionospheric Perturbations?
No full textPlasma depletion during a solar eclipse is well-documented, but the generation of other forms of ionospheric perturbations by the impact of eclipses is controversial. This study aims to evaluate the generation of additional ionospheric perturbations through case studies of total solar eclipses observed across the United States on 21 August 2017 and 8 May 2024. Total electron content (TEC) values are used to track ionospheric perturbations along the eclipse paths. When a smoothing filter (Savitzky-Golay filter) is applied to detect ionospheric perturbations, negative TEC perturbations are observed during totality, while positive TEC perturbations are detected around the beginning and end of the eclipses. These perturbations, caused by rapid TEC variations during these periods, are interpreted as filtering artifacts. Quasi-periodic multiple TEC perturbation layers are detected along the eclipse paths when an oscillatory filter (polynomial detrending) is applied. However, as this filter introduces wave-like artifacts during detrending, the resulting patterns do not represent actual TEC perturbations. Based on our observational and test results, we conclude that eclipse-induced ionospheric perturbations beyond the well-documented plasma depletion are not evident because actual eclipse-induced perturbations are not distinguishable from filtering artifacts.
Ionospheric Disturbances in Low‐ and Midlatitudes During the Geomagnetic Storm on 26 August 2018
No full textPlasma density depletions at midlatitudes during geomagnetic storms are often understood in terms of equatorial plasma bubbles (EPBs) due to their morphological similarity. However, our study reports the observations that reveal the generation of plasma depletions at midlatitudes by local sources. During the geomagnetic storm on 26 August 2018, the Defense Meteorological Satellite Program and Swarm satellites detected plasma depletions at midlatitudes in the Asian sector in the absence of EPBs in the equatorial region. This observation and the total electron content (TEC) maps over Japan demonstrate that traveling ionospheric disturbances (TIDs) are the sources of midlatitude plasma depletions in the Asian sector. Near the west coast of the United States, the development of a narrow TEC depletion band was identified from TEC maps. The TEC depletion band, which is elongated in the northwest-southeast direction, moves toward the west with a velocity of approximately 240 m/s. The TEC at the TEC depletion band is about 5 TEC units (10(16) m(-2)) smaller than the ambient TEC. As this band is confined to the midlatitudes, this phenomenon is not associated with an EPB. The characteristics of the TEC depletion band are consistent with those of medium-scale TIDs. Observations in the Asian sector and the TEC depletion band over the United States demonstrate that plasma depletions can develop at midlatitudes by local sources. Therefore, the morphological similarity between midlatitude irregularities and EPBs or their coincident occurrence does not provide corroborating evidence of their connection.
Assessment of the Origin of a Plasma Depletion Band Over the United States During the 8 September 2017 Geomagnetic Storm
No full textAbstract The development of an intense total electron content (TEC) depletion band over the United States during the 8 September 2017 geomagnetic storm was understood as the extension of an equatorial plasma bubble (EPB) to midlatitudes in previous studies. However, this study reports non‐EPB aspects within this phenomenon. First, the simultaneous emergence of the TEC depletion band at midlatitudes and EPBs in the equatorial region indicates that the midlatitude TEC depletion band is not initiated by an EPB. Second, the intensification of TEC depletion at midlatitudes during the decay of TEC depletion at intermediate latitudes is anomalous. Third, the location of the TEC depletion band at midlatitudes is inconsistent with the EPB location estimated from zonal plasma motion. Given ionospheric perturbations in North America from the beginning of the storm, it is plausible that the TEC depletion band was locally generated in association with these perturbations
The Origin of Midlatitude Plasma Depletions Detected During the 12 February 2000 and 29 October 2003 Geomagnetic Storms
No full textLarge amplitude plasma density irregularities have occasionally been detected at night in the midlatitude F region during geomagnetic storms. They are often interpreted in terms of equatorial plasma bubbles (EPBs) because midlatitude irregularities have the morphology of EPBs. This study assesses whether morphology can be a determining factor in ascribing the origin of such midlatitude ionospheric irregularities. We address this question by analyzing the observations of the First Republic of China satellite (ROCSAT-1) and Defense Meteorological Satellite Program (DMSP)-F14 and -F15 satellites during the geomagnetic storms on 12 February 2000 and 29 October 2003. On both days, ROCSAT-1 detects plasma depletions at midlatitudes in broad longitude regions and DMSP satellites detect isolated severe plasma depletions whose widths and depths are much wider and deeper than those of typical EPBs. The distinguishing characteristics during the storms are the detection of midlatitude depletions only in the Southern Hemisphere and the occurrence of some of these depletions before 19 hr local time and at the longitudes where EPBs are absent in the equatorial region. These characteristics are not explained satisfactorily by the characteristics of EPBs. Considering the detection of some of the midlatitude depletions at the equatorward edge of ionospheric perturbations in midlatitudes, midlatitude depletions are likely ionospheric perturbations that originated from higher latitudes. Because midlatitude depletions can originate from different sources, the morphology alone is not a determining factor of their origin.
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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