Variability of the African equatorial ionization anomaly (EIA) crests during the year 2013

Amaechi, P. O.; Oyeyemi, E. O.; Akala, A. O.

doi:10.1139/cjp-2017-0985

Cited by 10 publications

(8 citation statements)

References 45 publications

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“…In addition, the latitudinal position of the NC and SC saddled 17–22° geographic latitude (8.2–13.7°N magnetic latitude) and 2° to −11° geographic latitude (7.3–21.3°S magnetic latitude), respectively. It is important to recall that these variations are similar to those presented in Amaechi et al (2018c) but are more accurate in the present study because of the increased number of stations used and better latitudinal and temporal resolution. The new result is that the position of the T of the African EIA varies from 2.2°S to 3.0°N magnetic latitude and should not be assumed to be fixed as has been the case in several previous studies.…”

Section: Resultssupporting

confidence: 88%

Quiet Time Ionopheric Irregularities Over the African Equatorial Ionization Anomaly Region

Amaechi¹,

Oyeyemi

Akala

et al. 2020

Radio Science

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This paper investigated variations of quiet time ionospheric irregularities over the African equatorial ionization anomaly using the rate of change of total electron content index. Irregularities were quantified in terms of percentage occurrence and examined along with parameter of the anomaly, mainly its strength and the asymmetry of the crests as well as equatorial electric field derived from the real‐time equatorial electric field model and meridional wind obtained from the horizontal wind model. Irregularities occurred from 19:30 to 03:00 LT with a time difference of 1 hr between both crests. The highest occurrences were registered in April: 91.67%, 75.00%, and 96.43% for the northern crest, trough, and southern crest, respectively. Seasonally, stronger anomaly (>20 total electron content unit) in addition to the highest equatorial electric field value in the dusk sector corresponded with the equinoctial higher occurrence rate in both hemispheres, while stronger meridional wind and farthest crests location accounted for the least occurrence in winter. The summer occurrence rate was favored by reduced meridional wind, smaller crests location, and late time of prereversal enhancement at the magnetic equator. There was a significant asymmetry in irregularities over the crests in both hemispheres with stronger and greater occurrence rate over the southern crest. Also, irregularities strength and occurrence rate were similar over the northern crest and trough in summer. In addition to dusk‐sector activity, irregularities occurred during postmidnight in summer. Simultaneous variations of irregularities at the crests and trough also highlighted the contribution of nonequatorial processes to their formation at the crests.

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Section: Resultssupporting

confidence: 88%

Quiet Time Ionopheric Irregularities Over the African Equatorial Ionization Anomaly Region

Amaechi¹,

Oyeyemi

Akala

et al. 2020

Radio Science

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“…Also, the vertical plasma drift velocity (Vz) which results from the interaction of the eastward electric field and horizontal magnetic field play a significant role in the transport and redistribution of plasma at low-latitude. Vz is stronger in equinox than solstice over the African longitude (Amaechi et al, 2018;Fejer et al, 1995). The implication is that the fountain effect will be stronger in equinox and more plasma will be lifted up and diffused towards the crests.…”

Section: The Winter and Semiannual Anomaliesmentioning

confidence: 96%

“…It was computed in the local noon (1200 -1700 LT) and post sunset (1900 -2200 LT) using equation 1. Both time intervals correspond to periods when the anomaly is fully developed in Africa (Amaechi et al, 2018).…”

Section: Tec Derived From Iri Model (Iri-tec)mentioning

confidence: 99%

Comparison of ionospheric anomalies over African equatorial/low-latitude region with IRI-2016 model predictions during the maximum phase of solar cycle 24

Amaechi¹,

Oyeyemi

Akala

et al. 2021

Advances in Space Research

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The capability of IRI-2016 in reproducing the hemispheric asymmetry, the winter and semiannual anomalies has been assessed over the equatorial ionization anomaly (EIA) during quiet periods of years 2013-2014. The EIA reconstructed using Total Electron Content (TEC) derived from Global Navigation Satellite System was compared with that computed using IRI-2016 along longitude 25o -40oE. These were analyzed along with hemispheric changes in the neutral wind derived from the horizontal wind model and the TIMED GUVI columnar O/N2 data. IRI-2016 clearly captured the hemispheric asymmetry of the anomaly during all seasons albeit with some discrepancies in the magnitude and location of the crests. The winter anomaly in TEC which corresponded with greater O/N2 in the winter hemisphere was also predicted by IRI-2016 during December solstice. The model also captured the semiannual anomaly with stronger crests in the northern hemisphere. Furthermore, IRI-2016 reproduced the variation trend of the asymmetry index (A) in December solstice and equinox during noon. However, in June solstice the model failed to capture the winter anomaly and misrepresented the variation of A. This was linked with its inability to accurately predict the pattern of the neutral wind, the maximum height of the F2 layer and the changes in O/N2 in both hemispheres. The difference between variations of EUV and F10.7 fluxes was also a potential source of errors in IRI-2016. The results highlight the significance of the inclusion of wind data in IRI-2016 in order to enhance its performance over East Africa.

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“…Overall, we observed clear asymmetry in the distribution of ionospheric plasma over the African EIA NH and SH crests (Watthanasangmechai et al, 2015; Amaechi et al, 2019). Figure 6 shows the illustrations of how the influence of meridional neutral wind leads to EIA asymmetry in the F layer of the ionosphere.…”

Section: Resultsmentioning

confidence: 99%

“…Generally, with respect to diurnal and seasonal variations of the African EIA structures, our results were consistent with the results earlier reported by Kassa et al (2014), Opio et al (2015), Oryema et al (2016), Bolaji et al (2017), and Amaechi et al (2019), although each set of authors above analyzed data for only 1 year. In addition to the fact that the current study covered more data for a more robust climatology study of the African EIA structures, this study also revealed new information about the daily morphologies of the African EIA structures, starting from the EIA formative, fully formed, and decaying stages, and also the intrahemispherical and interhemispherical plasma transport within the African EIA region.…”

Section: Resultsmentioning

confidence: 99%

Characterization of African Equatorial Ionization Anomaly During the Maximum Phase of Solar Cycle 24

2020

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This study characterizes the African equatorial ionization anomaly (EIA) during the maximum phase of Solar Cycle 24 (2012-2015). Total electron content (TEC) data were obtained from a chain of 13 African Global Navigation Satellite System (GNSS) receivers (within 36-42°E geographic longitude; 29°N to 10°S geographic latitude; ±20°N magnetic latitude) to study quiet time variations of TEC and thereafter construct the EIA profiles. The correlations of TEC for pairs of conjugate stations within the African EIA were determined. TEC station-to-trough ratio (TEC-STR) was used as an index to determine the strength of the EIA crests. Furthermore, the variability of the EIA crests on a 3-hourly basis over each month was investigated. Overall, equinoxes recorded the highest values of TEC, with the widest latitudinal location of the EIA crests, and June solstice recorded the least, with the characteristic equatorward collapse of the EIA crests. TEC and the location of the crests of the EIA also increased with solar activity. TEC showed good correlations for conjugate pairs of stations, especially for stations closer to the trough. The African EIA morphology showed asymmetry in the locations of the Northern Hemisphere (NH) and Southern Hemisphere (SH) crests. The formation of EIA starts around 0600-0800 LT and decays around 2100-2300 LT. Generally, SH crest forms first before NH crest and also decays first; we attributed this to the effects of the meridional neutral winds. Comparing TEC at African EIA crests with other longitudinal sectors, the Asian sector recorded the highest TEC, while the American sector recorded the least.

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Variability of the African equatorial ionization anomaly (EIA) crests during the year 2013

Cited by 10 publications

References 45 publications

Quiet Time Ionopheric Irregularities Over the African Equatorial Ionization Anomaly Region

Quiet Time Ionopheric Irregularities Over the African Equatorial Ionization Anomaly Region

Comparison of ionospheric anomalies over African equatorial/low-latitude region with IRI-2016 model predictions during the maximum phase of solar cycle 24

Characterization of African Equatorial Ionization Anomaly During the Maximum Phase of Solar Cycle 24

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