Equatorial electrojet and regular daily variation SR—III. Comparison of observations with a physical model

Fambitakoye, O.; Mayaud, Pierre-Noël; Richmond, A. D.

doi:10.1016/0021-9169(76)90118-5

Cited by 62 publications

(31 citation statements)

References 13 publications

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“…3A) for instance, a minimum value in the H variation is clearly visible at the Nielle (NIE), Sikasso (SIK) and Koutiala (KOU) stations prior to the beginning of the typical S R E variation. This minimum marks the presence of a morning counter electrojet (Gouin and Mayaud, 1967;Fambitakoye and Mayaud, 1976c) which was not clearly marked at the other stations because of the latitudinal asymmetry of the counter-electrojet with respect to the dip equator.…”

Section: Quiet Magnetic Situationsmentioning

confidence: 93%

“…The magnetic variations recorded during 171 quiet or almost-quiet days were digitized at the nine stations. An analysis of this unique magnetic data set resulted in an important contribution to the understanding of the temporal and spatial behavior of the equatorial electrojet (Fambitakoye, 1976;Fambitakoye and Mayaud, 1976a, b, c;Fambitakoye et al, 1976). In particular, the experiment provided quite clear experimental evidence that the internal part of the observed diurnal variation in the S R E of the magnetic ®eld is very weak, and practically negligible in the equatorial electrojet region (Fambitakoye and Mayaud, 1973;.…”

Section: Introductionmentioning

confidence: 99%

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A study of transient variations in the Earth's electromagnetic field at equatorial electrojet latitudes in western Africa (Mali and the Ivory Coast)

Vassal

Menvielle

Cohen³

et al. 1998

Ann. Geophys.

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Abstract. In the framework of the French-Ivorian participation to the IEEY, a network of 10 electromagnetic stations were installed at African longitudes. The aim of this experiment was twofold: ®rstly, to study the magnetic signature of the equatorial electrojet on the one hand, and secondly, to characterize the induced electric ®eld variations on the other hand. The ®rst results of the magnetic ®eld investigations were presented by Doumouya and coworkers. Those of the electric ®eld experiment will be discussed in this study. The electromagnetic experiment will be described. The analysis of the electromagnetic transient variations was conducted in accordance with the classical distinction between quiet and disturbed magnetic situations. A morphological analysis of the recordings is given, taking into consideration successively quiet and disturbed magnetic situations, with the results interpreted in terms of the characterization of external and internal sources. Particular attention was paid to the e ects of the source characteristics on the induced ®eld of internal origin, and to the bias they may consequently cause to the results of electromagnetic probing of the Earth; the source e ect in electromagnetic induction studies. During quiet magnetic situations, our results demonstrated the existence of two di erent sources. One of these, the S R E source, was responsible for most of the magnetic diurnal variation and corresponded to the well-known magnetic signature of the equatorial electrojet. The other source (the S *E R source) was responsible for most of the electric diurnal variation, and was also likely to be an ionospheric source. Electric and magnetic diurnal variations are therefore related to di erent ionospheric sources, and interpreting the electric diurnal variation as induced by the magnetic ®eld diurnal variation is not relevant. Furthermore, the magnetotelluric probing of the upper mantle at dip equator latitudes with the electromagnetic diurnal variation is consequently impossible to perform. In the case of irregular variations, the source e ect related to the equatorial electrojet is also discussed. A Gaussian model of equatorial electrojet was considered, and apparent resistivities were computed for two models of strati®ed Earth corresponding to the average resistive structure of the two tectonic provinces crossed by the pro®le: a sedimentary basin and a cratonic shield. The apparent resistivity curves were found to depend signi®cantly on both the model used and the distance to the center of the electrojet. These numerical results con®rm the existence of a daytime source e ect related to the equatorial electrojet. Furthermore, we show that the results account for the observed di erences between daytime and night-time apparent resistivity curves. In particular, it was shown that electromagnetic probing of the Earth using the classical Cagniard-Tikhonov magnetotelluric method is impossible with daytime recordings made at dip latitude stations.

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Section: Quiet Magnetic Situationsmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

A study of transient variations in the Earth's electromagnetic field at equatorial electrojet latitudes in western Africa (Mali and the Ivory Coast)

Vassal

Menvielle

Cohen³

et al. 1998

Ann. Geophys.

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“…FAMBITAKOYE and MAYAUD (1976c) have gone on to demonstrate the variability from day-to-day of the regular daily variation SR, which is attributed to the presence of the counter electrojet and to neutral winds in the equatorial ionosphere. FAMBITAKOYE et al (1976) have demonstrated that east-west winds can create current flow opposed to the primary electrojet, and that these winds augment the planetary component of SR around midday over values produced purely by magnetospheric electric fields. Finally, we note that MAYAUD (1976c) has failed to find evidence of regular variations of the magnetic field at ground level which OLSON (1970) predicted should result from magnetopause, neutral sheet and ring current effects and should be measurable at quiet times.…”

Section: Magnetic and Electric Fields And Current Flow At Middle And mentioning

confidence: 97%

Electric and magnetic fields in the ionosphere and magnetosphere.

Rostoker

1978

J. geomagn. geoelec

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Recent observations of electric fields in the ionosphere using various measurement techniques have led to important advances in the understanding of magnetosphere-ionosphere coupling. In particular the discovery of evidence for parallel electric fields in the altitude range 2,000-10,000 km has an important impact on the question of auroral acceleration processes. More detailed mapping of large scale field-aligned current configurations on field lines penetrating the auroral oval are leading to more complete models for the generator processes in the outer magnetosphere which are associated with energy dissipation in the near-earth environment. Recent observations of significant electric fields equatorward of the auroral oval indicate that significant interaction between the magnetosphere and ionosphere takes place outside of the auroral oval. New techniques are presently being developed for more quantitative studies of magnetosphere-ionosphere coupling.

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“…The parameters s and J DC are determined by least-squares inversion of equation (12), under the constraint that the left and right hand sides of that equation must agree at the dip equator (y = p/2). This constraint has been found to yield more accurate electric fields [Alken and Maus, 2010b], since the EEF is primarily responsible for current structure near the dip equator, while the winds are primarily responsible for current structure at higher latitudes [Fambitakoye et al, 1976].…”

Section: Modeling the Equatorial Electrojet Currentmentioning

confidence: 99%

Longitudinal and seasonal structure of the ionospheric equatorial electric field

Alken¹,

Chulliat

Maus³

2013

JGR Space Physics

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[1] The daytime eastward equatorial electric field (EEF) in the ionospheric E-region plays an important role in equatorial ionospheric dynamics. It is responsible for driving the equatorial electrojet (EEJ) current system, equatorial vertical ion drifts, and the equatorial ionization anomaly. Due to its importance, there is much interest in accurately measuring and modeling the EEF. In this work we propose a method of estimating the EEF using CHAMP satellite-derived latitudinal current profiles of the daytime EEJ along with Δ H measurements from ground magnetometer stations. Magnetometer station pairs in both Africa and South America were used for this study to produce time series of electrojet current profiles. These current profiles were then inverted for estimates of the EEF by solving the governing electrostatic equations. We compare our results with the Ion Velocity Meter (IVM) instrument on board the Communication/Navigation Outage Forecasting System satellite. We find high correlations of about 80% with the IVM data; however, we also find a constant offset of about 0.3 mV/m between the two data sets in Africa. Further investigation is needed to determine its cause. We compare the EEF structure in Africa and South America and find differences which can be attributed to the effect of atmospheric nonmigrating tides. This technique can be extended to any pair of ground magnetometer stations which can capture the day-to-day strength of the EEJ.Citation: Alken, P., A. Chulliat, and S. Maus (2013), Longitudinal and seasonal structure of the ionospheric equatorial electric field,

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Equatorial electrojet and regular daily variation SR—III. Comparison of observations with a physical model

Cited by 62 publications

References 13 publications

A study of transient variations in the Earth's electromagnetic field at equatorial electrojet latitudes in western Africa (Mali and the Ivory Coast)

A study of transient variations in the Earth's electromagnetic field at equatorial electrojet latitudes in western Africa (Mali and the Ivory Coast)

Electric and magnetic fields in the ionosphere and magnetosphere.

Longitudinal and seasonal structure of the ionospheric equatorial electric field

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