Equatorial electrojet and regular daily variation SR—I. A determination of the equatorial electrojet parameters

Fambitakoye, O.; Mayaud, Pierre-Noël

doi:10.1016/0021-9169(76)90188-4

Cited by 108 publications

(86 citation statements)

References 3 publications

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“…Similar curves were shown by Fambitakoye and Mayaud (1976) for the H, Z and D data at the chain of stations in the Central African sector operating in 1968-1970. Figure 13 is drawn after the Fig.…”

Section: Latitudinal Variations Of X Y and Z For Different Local Hourssupporting

confidence: 77%

“…These pairs of stations have been shown to be Huancayo, Fuquene for American and Trivandrum, Alibag for Indian longitudes (Rastogi et al, 1977). Fambitakoye and Mayaud (1976) have made their analyses separating the observed daily variations of the magnetic H and Z fields into components: one corresponding to the electrojet current flowing within a narrow band along the dip equator and the remainder due to the component of a planetary current system.…”

Section: Two Sheets Of Currents In the E-region Above The Dip Equatormentioning

confidence: 99%

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Asymmetries in the equatorial electrojet around N-E Brazil sector

Rastogi

Trivedi²

2009

Ann. Geophys.

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Abstract. The paper examines the data of geographic northward (X), eastward (Y) and vertical (Z) components of the magnetic field from a dense array of 26 vector magnetometers operated in N-NE Brazil from November 1990 to March 1991. As expected, the daily variation of X showed a minor maximum around 03:00-04:00 LT and a major maximum around 12:00 LT. The daily range of Y showed a strong minimum around noon at all stations. The combined Y and X indicated the direction of the equatorial electrojet currents to be flowing along 25 • north of east at the centre and 20 • north of east at the edges of the equatorial electrojet (EEJ) belt. The centre of the EEJ as defined by the zero intercept of the Z versus latitude was found to be near 1.0 • S dip latitude. The electrojet current was stronger in the northern half than in the southern half of the electrojet belt. These anomalies are suggested to be due to the abnormal distribution of the mean magnetic field in this region.

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Section: Latitudinal Variations Of X Y and Z For Different Local Hourssupporting

confidence: 77%

Section: Two Sheets Of Currents In the E-region Above The Dip Equatormentioning

confidence: 99%

Asymmetries in the equatorial electrojet around N-E Brazil sector

Rastogi

Trivedi²

2009

Ann. Geophys.

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“…It is now well established that the Earth's magnetic ®eld has a fairly simple behavior for the frequencies considered in this study [from about 10 cph (cycle per hour) to 1 cpd (cycle per day)] (see, e.g., Chapman, 1951;Fambitakoye and Mayaud, 1976a). In contrast, the behavior of transient variations in the electric ®eld in equatorial regions was poorly understood before the present study.…”

Section: The Observed Electromagnetic Variationsmentioning

confidence: 72%

“…Given the latitudinal extent of the equatorial electrojet (see this study, Sect. 3.3, and e.g., Fambitakoye and Mayaud, 1976a;Onwumechilli and Ozoemena, 1985;Doumouya et al, 1997), the plane wave approximation no longer holds for frequencies smaller than a few cph, such that interpretation of daytime electromagnetic observations must take into account the actual distribution of ionospheric currents at equatorial latitudes. The variation of the E-W current density with latitude has been studied for decades.…”

Section: Induction By the Irregular Variationsmentioning

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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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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“…At equatorial latitudes atmospheric tides play a significant role in controlling both the neutral dynamics and the electrodynamics of the MLT region. The equatorial electrojet (EEJ), a unique geophysical phenomenon over the magnetic equator, is an outcome of the tidal diurnal wind-driven dynamo on a global scale [Fambitakoye and Mauyaud, 1976;Forbes, 1981].…”

Section: Introductionmentioning

confidence: 99%

Planetary wave-tidal interactions over the equatorial mesosphere-lower thermosphere region and their possible implications for the equatorial electrojet

et al. 2011

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[1] Optically measured daylight mean mesopause temperatures over a dip equatorial station, Trivandrum (8.5°N; 77°E; dip lat. 0.5°N), have been analyzed in conjunction with simultaneously measured equatorial electrojet (EEJ)-produced magnetic field at the surface. The signature of planetary wave-tidal interactions in the mesosphere-lower thermosphere (MLT) region has been observed for the first time in the day-to-day variability in the EEJ, i.e., the time of its peaking and the duration, as inferred from the EEJ-produced magnetic field on the ground. The present study shows that the planetary wave of quasi 16 day periodicity plays an important role in causing these variabilities, especially during the winter months. The quasi 16 day wave is found to be modulating the mesopause temperature (MT), duration, and time of the maximum EEJ intensity (D EEJ and T EEJ ). During positive excursions of the planetary wave, T EEJ showed a shift toward evening, while the MT showed an increase and D EEJ showed a broadening. Similarly, all these parameters exhibited an opposite trend during negative excursions. The planetary wave-tidal interactions and subsequent modification of the tidal components have been shown to be responsible for the observed variations. This study presents a new perspective addressing the day-to-day variability of the EEJ.

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Equatorial electrojet and regular daily variation SR—I. A determination of the equatorial electrojet parameters

Cited by 108 publications

References 3 publications

Asymmetries in the equatorial electrojet around N-E Brazil sector

Asymmetries in the equatorial electrojet around N-E Brazil sector

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

Planetary wave-tidal interactions over the equatorial mesosphere-lower thermosphere region and their possible implications for the equatorial electrojet

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