Equatorial ionospheric electron density below the <i>F</i><sub>2</sub> peak

Radicella, S. M.; Adeniyi, J.O.

doi:10.1029/1999rs900071

Cited by 52 publications

(46 citation statements)

References 12 publications

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“…From our results that showed a maximum magnitude of ∼ 49 nT around 12:00 LT associated with a significant CEJ (∼ 48 nT) around 09:00 LT, this EEJ strength variability (7 April) indicates a weaker eastward daytime electric field during sunrise hours and that a pre-noon EIA crest could not be formed. Investigations into pre-noon peaks of TEC and electron density at the F2-layer (NmF2) over the equatorial latitudes have been made by Skinner (1966), Rajaram (1977), Radicella and Adeniyi (1999), Lee and Reinisch (2006), and Bolaji et al (2012Bolaji et al ( , 2013. They reported that development of a prenoon EIA crest is due to a stronger eastward daytime electric field compared to photoionization near noon.…”

Section: Discussionmentioning

confidence: 99%

Observations of equatorial ionization anomaly over Africa and Middle East during a year of deep minimum

et al. 2017

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Abstract. In this work, we investigated the veracity of an ion continuity equation in controlling equatorial ionization anomaly (EIA) morphology using total electron content (TEC) of 22 GPS receivers and three ground-based magnetometers (Magnetic Data Acquisition System, MAGDAS) over Africa and the Middle East (Africa-Middle East) during the quietest periods. Apart from further confirmation of the roles of equatorial electrojet (EEJ) and integrated equatorial electrojet (IEEJ) in determining hemispheric extent of EIA crest over higher latitudes, we found some additional roles played by thermospheric meridional neutral wind. Interestingly, the simultaneous observations of EIA crests in both hemispheres of Africa-Middle East showed different morphology compared to that reported over Asia. We also observed interesting latitudinal twin EIA crests domiciled at the low latitudes of the Northern Hemisphere. Our results further showed that weak EEJ strength associated with counter electrojet (CEJ) during sunrise hours could also trigger twin EIA crests over higher latitudes.

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Section: Discussionmentioning

confidence: 99%

Observations of equatorial ionization anomaly over Africa and Middle East during a year of deep minimum

et al. 2017

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“…Earlier studies (e.g., Rajaram and Rastogi, 1977;Radicella and Adeniyi, 1999) suggested that the bite-out is pronounced around the F2 layer and it is due to the vertical transport of F region plasma. Total electron content observations have not revealed noon bite-out, suggesting that the noon bite-out is primarily related to the F2 layer (e.g., Lee, 2012, and references therein).…”

Section: Local Time Variations In F Of2 and F Of3mentioning

confidence: 99%

Ionospheric variations over Indian low latitudes close to the equator and comparison with IRI-2012

et al. 2015

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Abstract.In this paper, we analyze daytime observations of the critical frequencies of the F2 (f oF2) and F3 (f oF3) layers based on ionosonde observations made from Indian low latitudes close to the magnetic equator and study their local time, seasonal, planetary-scale variations (including the solar rotation effect), and solar activity dependence. Given the occurrence of the F3 layer, which has remarkable local time, seasonal and solar activity dependences, variations in f oF2 have been evaluated. Local time variations in f oF2 and f oF3 show noon "bite-out" in all seasons and in all solar activity conditions, which are attributed to vertically upward plasma transport by the zonal electric field and meridional neutral wind. Comparison of observed f oF2 with those of the IRI-2012 model clearly shows that the model values are always higher than observed values and the largest difference is observed during noontime owing to the noon bite-out phenomenon. Peak frequency of the F layer (f oF2 / f oF3), however, is found to have better agreement with IRI-2012 model. Seasonal variations of f oF2 and f oF3 show stronger asymmetry at the solstices than at the equinoxes. The strong asymmetry at the solstice is attributed to the asymmetry in the meridional neutral wind with a secondary contribution from E × B drifts, and the relatively weak asymmetry observed at the equinox is attributed to the asymmetry in E × B drifts. Variations in f oF2 and f oF3 with solar flux clearly show the saturation effect when F 10.7 exceeds ∼ 120 sfu, which is different from that of the mid-latitudes. Irrespective of solar flux, both f oF2 and f oF3 in summer, however, are found to be remarkably lower than those observed in other seasons. Variations in f oF2 show dominant periods of ∼ 27, ∼ 16 and ∼ 6 days. Intriguingly, amplitudes of ∼ 27-day variations in f oF2 are found to be maximum in low solar activity (LSA), moderate in medium solar activity (MSA) and minimum in high solar activity (HSA), while the amplitudes of ∼ 27-day variations in F 10.7 are minimum in LSA, moderate in MSA and maximum in HSA. These results are presented and discussed in light of current observational and modelbased knowledge on the variations of low-latitude f oF2 and f oF3.

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“…Again, Oyekola (2011) indicated that drift velocity predicted for Ibadan longitude sector by the latest version of IRI (IRI-2007) could be used to explain the observed daily features of f o F 2 at the African equatorial site of Ibadan for some selected months during the year 1958 (IGY-era) under sunspot maximum conditions. Furthermore, most of the observed features and behavior of equatorial ionospheric F 2 -layer parameters in the African sector and other equatorial stations around the world have been attributed mostly to variations of vertical V z = E × B plasma drift (e.g., Sambou et al, 1998;Radicella and Adeniyi, 1999).…”

Section: Introductionmentioning

confidence: 99%

Equatorial vertical plasma drifts and the measured and IRI model-predicted F 2-layer parameters above Ouagadougou during solar minimum

Oyekola¹

2012

Earth Planet Sp

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In this paper, hourly median value of ionosonde measurements: peak height F 2 -layer (h m F 2 ), F 2 -layer critical frequency ( f o F 2 ) and propagation factor M(3000)F 2 made at near-equatorial dip latitude, Ouagadougou, Burkina Faso (12• N, 1.5 • W; dip: 1.5• N) and relevant F 2 -layer parameters: thickness parameter (B o ), electron temperature (T e ), ion temperature (T i ), total electron content (TEC) and electron density (N e ) (at the fixed altitude of 300 km) provided by the International Reference Ionosphere (IRI) model for the longitude of Ouagadougou are contrasted with the IRI vertical drift model to explore in detail the monthly climatological behavior of equatorial ionosphere and the effects of equatorial electrodynamics on the diurnal structure of F 2 -layer parameters. The analysis period covers four months representative of solstitial and equinoctial seasonal periods during solar minimum year of 1987 for geomagnetically quiet-day. It is demonstrated that the month-by-month morphological patterns between vertical E × B drifts and F 2 -layer parameters range from worst to reasonably good and are largely seasonally dependent. A cross-correlation analysis conducted between equatorial drift and F 2 -layer characteristics yield statistically significant correlations for equatorial vertical drift and IRI-B o , IRI-T e and IRI-TEC, whereas little or no acceptable correlation is obtained with observational evidence. Examination of the association between measured f o F 2 , h m F 2 and M(3000)F 2 illustrates consistent much more smaller correlation coefficients with no systematic linkage.

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Equatorial ionospheric electron density below the F₂ peak

Cited by 52 publications

References 12 publications

Observations of equatorial ionization anomaly over Africa and Middle East during a year of deep minimum

Observations of equatorial ionization anomaly over Africa and Middle East during a year of deep minimum

Ionospheric variations over Indian low latitudes close to the equator and comparison with IRI-2012

Equatorial vertical plasma drifts and the measured and IRI model-predicted F 2-layer parameters above Ouagadougou during solar minimum

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Equatorial ionospheric electron density below the F2 peak

Cited by 52 publications

References 12 publications

Observations of equatorial ionization anomaly over Africa and Middle East during a year of deep minimum

Observations of equatorial ionization anomaly over Africa and Middle East during a year of deep minimum

Ionospheric variations over Indian low latitudes close to the equator and comparison with IRI-2012

Equatorial vertical plasma drifts and the measured and IRI model-predicted F 2-layer parameters above Ouagadougou during solar minimum

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Equatorial ionospheric electron density below the F₂ peak