Latitudinal extent of the equatorial electrojet.

Onwumechili, C. Agodi; Ozoemena, P. C.

doi:10.5636/jgg.37.193

Cited by 11 publications

(9 citation statements)

References 17 publications

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“…ONWUMECHILI and OZOEMENA (1985) had also noted the same situation with regard to the half width w and the latitudinal extent L, of the EEJ. CAIN and SWEENEY (1972) pointed out that latitudinal profiles of the EEJ are wider at greater altitudes and this has been reflected in all our expressions of the distances by v, the altitude of EEJ.…”

Section: Vertical Magnetic Field Componentmentioning

confidence: 81%

“…With values of Jo, a and a determined by Onwumechili and Agu and given in ONWUMECHILI and AGU (1981) and ONWUMECHILI and OZOEMENA (1985), we of the minimum intensity Jm to the maximum intensity Jo is also given in Table 1 in percentage.…”

Section: Minimum Current Intensitymentioning

confidence: 99%

“…Here a again came out negative, and in reasonable agreement with its value from ground data. ONWUMECHILI and OZOEMENA (1985) applied the principle of continuity of current to the model, and found that for the current to be nondivergent, a<-1.…”

Section: Minimum Current Intensitymentioning

confidence: 99%

“…For the POGO equinox data ONWUMECHILI and AGU (1981) have studied the peak eastward current intensity Jo, at the axis of the EEJ above the magnetic dip equator at x=0, while ONWUMECHILI and OZOEMENA (1985) studied the meridional scale length a and the meridional distribution parameter a which controls the distribution of current along a meridian. With values of Jo, a and a determined by Onwumechili and Agu and given in ONWUMECHILI and AGU (1981) and ONWUMECHILI and OZOEMENA (1985), we of the minimum intensity Jm to the maximum intensity Jo is also given in Table 1 in percentage.…”

Section: Minimum Current Intensitymentioning

confidence: 99%

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Landmark values of equational electrojet current and magnetic field along a meridian near noon.

Onwumechili

Ozoemena

Agu

1989

J. geomagn. geoelec

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Landmark values of the equatorial electrojet: the minimum intensity Jm A.km-1, its distance xm km and ratio to maximum intensity Jm/Jo; the magnetic field constant K nT; the maximum northward magnetic field Xo nT, and the distance of zero northward magnetic field wx km; the minimum northward magnetic field Xm nT, its distance um km and ratio to maximum northward field Xm/Xo; the vertical magnetic field Zo nT at the dip equator and the distance of zero vertical field wz km; the maximum vertical magnetic field ZM nT, its distance uM km and ratio to maximum northward field Zm/Xo; have all been derived from September equinox satellite data and they compare favourably with their values from ground-based data. Our Jm/Jo agrees excellently with MUSMANN and SEILER (1978) and ANANDARAO and RAGHAVARAO (1979); while our xm agrees excellently with the location of CAHILL's (1959) westward current, and the findings of MUSMANN and SEILER (1978). The landmark distances xm, wx, um, uM, wz and the ratios Jm/Jo, Xm/Xo and ZM/ Xo do not vary with longitude but the intensity Jm and magnetic fields, K, Xo, Xm, Zo and

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Section: Vertical Magnetic Field Componentmentioning

confidence: 81%

Section: Minimum Current Intensitymentioning

confidence: 99%

Section: Minimum Current Intensitymentioning

confidence: 99%

Section: Minimum Current Intensitymentioning

confidence: 99%

See 2 more Smart Citations

Landmark values of equational electrojet current and magnetic field along a meridian near noon.

Onwumechili

Ozoemena

Agu

1989

J. geomagn. geoelec

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“…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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Subsolar Elevation of the Equatorial Electrojet

Onwumechili¹,

Ozoemena²

1989

Quiet Daily Geomagnetic Fields

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Latitudinal extent of the equatorial electrojet.

Cited by 11 publications

References 17 publications

Landmark values of equational electrojet current and magnetic field along a meridian near noon.

Landmark values of equational electrojet current and magnetic field along a meridian near noon.

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

Subsolar Elevation of the Equatorial Electrojet

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