Climatology of GPS amplitude scintillations over equatorial Africa during the minimum and ascending phases of solar cycle 24

Akala, A. O.; Amaeshi, L. L. N.; Somoye, E.O.; Idolor, Raphael; Okoro, Emeka Emmanuel; Doherty, Patricia H.; Groves, K. M.; Carrano, Charles S.; Bridgwood, C.; Baki, P.; D’ujanga, Florence Mutonyi; Seemala, G. K.

doi:10.1007/s10509-015-2292-9

Cited by 22 publications

(17 citation statements)

References 30 publications

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“…Taking the reduced data availability into account, the results are in line with other observations showing maxima of plasma bubble occurrence rate during equinox months (e.g., Blanch et al, 2018;Magdaleno et al, 2017). These plasma depletions, in turn, are associated with the maximum occurrence of scintillations in the African low-latitude ionosphere, as also indicated in the studies by Hlubek et al (2014) and Akala et al (2015). Our method for the automatic detection of plasma bubbles is comparable to a great extent with the detection techniques developed by Nishioka et al (2008) and Blanch et al (2018).…”

Section: Application Of the Methodssupporting

confidence: 90%

A Method for Automatic Detection of Plasma Depletions by Using GNSS Measurements

et al. 2020

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Enhanced scintillation activities observed at transionospheric radio signals are often correlated with slant total electron content (STEC) depletions in the equatorial ionosphere. In this study, the data derived from high‐rate Global Navigation Satellite System (GNSS) receivers were used to analyze the observed STEC depletions, commonly associated with plasma bubbles causing radio scintillations in the equatorial ionosphere. We found that the observed STEC depletion can be described by a wedge‐shaped structure. To quantitatively describe the structure of STEC depletions, we developed an effective method to routinely characterize the depth and the width of equatorial plasma depletion in automatized data screening. The developed method has been validated by analyzing data obtained from mostly African GNSS stations in 2014 and 2015. The results confirm current knowledge regarding the seasonal occurrence of radio scintillations and related bubbles. The detection results are compared with those from other published plasma bubble detection techniques.

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Section: Application Of the Methodssupporting

confidence: 90%

A Method for Automatic Detection of Plasma Depletions by Using GNSS Measurements

et al. 2020

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“…It was surprising to observe scintillation events during the month of January 2014, in contrast to Akala et al . [, ] who reported January as off‐season for equatorial scintillations at other locations in Africa, although the trends of occurrences were similar for other months at Dakar in comparison to these other locations in Africa (Lagos, Kampala, and Nairobi) [ Akala et al ., ]. The comparison of results from Akala et al .…”

Section: Resultsmentioning

confidence: 97%

“…Overall, the daily distributions of intense scintillations over Dakar were sparse or nonexistent during the hours of 18–20 and 02–06 LT but densely distributed within the hours of 20–02 LT. These results are in agreement with previous studies [ Aarons , ; Basu et al ., , ; Akala et al ., , , ].…”

Section: Resultsmentioning

confidence: 99%

“…The dual‐frequency technique is being used to address the concerns of group delay, while the concerns of scintillations, particularly; equatorial scintillation effects are not yet resolved [ Groves et al ., ; Sreeja et al ., ]. Toward this end, ICAO has mandated all of its regions, under the auspices of regional Ionospheric Studies Task Force (ISTF) to establish a framework for understanding the phenomenology of ionospheric scintillations in each region, with a view to proffering mitigation strategies to scintillation impacts on GNSS systems [ Akala et al ., ]. In this regard, the ISTF in ICAO's Africa‐Indian Ocean region has not been able to achieve this mandate due to lack of documented studies on the climatology of African ionospheric scintillation, which could be attributed to the absence of ionospheric observation stations in the continent over the past years.…”

Section: Introductionmentioning

confidence: 99%

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Statistics of GNSS amplitude scintillation occurrences over Dakar, Senegal, at varying elevation angles during the maximum phase of solar cycle 24

2016

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This study characterizes Global Navigation Satellite System amplitude scintillation over Dakar (14.75°N, 17.45°W, magnitude latitude: 5.88°N), Senegal. The data, which we arranged on daily and monthly scales, cover The data were further binned into three levels of scintillation using the S4 index: weak (0.3 ≤ S4 < 0.4), moderate (0.4 ≤ S4 < 0.7), and intense (S4 ≥ 0.7), over varying elevation angles (10°, 20°, and 30°). Daily occurrences of scintillation were most frequent around 22-02 LT. On a month-by-month basis, October recorded the highest occurrences of scintillations, while June recorded the least. Furthermore, contrary to Akala et al. (2014Akala et al. ( , 2015 who earlier reported January as off season for scintillation occurrences at some sites in Africa, namely, Lagos (Central West Africa), Nairobi, and Kampala (East Africa), the current study recorded some scintillation occurrences at Dakar (far west of West Africa) in January. It therefore implies that longitudinal variations do exist in the climatology of ionospheric scintillations over Africa. Consequently, detailed understanding of the climatology and daily distributions of ionospheric scintillations over equatorial Africa, which is our key objective in this study (from the perspective of Dakar), is the basic requirement for developing robust physics-based scintillation models for the African equatorial region. Finally, we noted that the conventional adoption of high-elevation masking angles during scintillation data processing, with a view to suppressing multipath effects usually hid important ionospheric-induced scintillation data.

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“…The work of Aarons (1982) clearly depicts how the scintillation intensities, produced by the smaller-scale irregularity structures coexisting with the plasma bubbles, are maximized in the regions of the Appleton anomaly. More recently, relevant features of ionospheric radio-wave scintillations at the equatorial anomaly region have been extensively investigated for different longitudinal sectors (Spogli et al, 2013;Chatterjee and Chakraborty, 2013;Bhattacharyya et al, 2014;Akala et al, 2015;Cesaroni et al, 2015;Zhang et al, 2015;Srinivasu et al, 2016;Moraes et al, 2017). In the South American sector, particularly for the L-band frequencies, the occurrence characteristics of scintillation-producing irregularities have been demonstrated using ground-based global navigation satellite system (GNSS) receiver networks (e.g., de Akala et al, 2011;Muella et al, 2013Muella et al, , 2014.…”

Section: Introductionmentioning

confidence: 99%

Climatology and modeling of ionospheric scintillations and irregularity zonal drifts at the equatorial anomaly crest region

et al. 2017

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Abstract. In this study the climatology of ionospheric scintillations and the zonal drift velocities of scintillationproducing irregularities are depicted for a station located under the southern crest of the equatorial ionization anomaly. Then, the α−µ ionospheric fading model is used for the firstand second-order statistical characterization of amplitude scintillations. In the statistical analyzes, data are used from single-frequency GPS receivers acquired during ∼ 17 years (September 1997-November 2014 at Cachoeira Paulista (22.4 • S; 45.0 • W), Brazil. The results reveal that the nocturnal occurrence of scintillations follows the seasonal distribution of plasma bubble irregularities observed in the longitudinal sector of eastern South America. In addition to the solar cycle dependence, the results suggest that the occurrence climatology of scintillations is also modulated by the secular variation in the dip latitude of Cachoeira Paulista, since the maximum occurrence of scintillations during the peak of solar cycle 24 was ∼ 20 % lower than that observed during the maximum of solar cycle 23. The dynamics of the irregularities throughout a solar cycle, as investigated from the estimates of the mean zonal drift velocities, presented a good correlation with the EUV and F10.7 cm solar fluxes. Meanwhile, the seasonal behavior showed that the magnitude of the zonal drift velocities is larger during the December solstice months than during the equinoxes. In terms of modeling, the results for the α − µ distribution fit quite well with the experimental data and with the temporal characteristics of fading events independently of the solar activity level.

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Climatology of GPS amplitude scintillations over equatorial Africa during the minimum and ascending phases of solar cycle 24

Cited by 22 publications

References 30 publications

A Method for Automatic Detection of Plasma Depletions by Using GNSS Measurements

A Method for Automatic Detection of Plasma Depletions by Using GNSS Measurements

Statistics of GNSS amplitude scintillation occurrences over Dakar, Senegal, at varying elevation angles during the maximum phase of solar cycle 24

Climatology and modeling of ionospheric scintillations and irregularity zonal drifts at the equatorial anomaly crest region

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