Internal induction by the equatorial electrojet in India examined with surface and satellite geomagnetic observations

Yacob, A.

doi:10.1016/0021-9169(77)90070-8

Cited by 17 publications

(13 citation statements)

References 10 publications

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“…The scatter is symmetrically distributed about the mean regression line, and the correlation coefficient is 0.86 in both Indian and American sectors. This compares favorably with the results of Yacob [1977], who found correlation coefficient of around 0.88 between the surface electrojet strength observed in the Indian region, extrapolated to the satellite height using a parabolic currentband model of electrojet, and the strength as obtained from satellite measurements. These correlations for the given number of points are significant at 99.9% level.…”

Section: Comparison Between Satellite and Ground Observationssupporting

confidence: 88%

“… Fambitakoye and Mayaud [1976] found no measurable induction of the electrojet field in Central Africa, while Ducruix et al [1977] have shown theoretically that electrojet‐induced field is negligible at least along the noon meridian. Yacob [1977] examined internal induction by the EEJ in India with ground and Pogo satellite geomagnetic observations and found that its internal field contribution is small. This could be regarded as some justification for neglecting geomagnetic induction.…”

Section: Determination Of Eej Parametersmentioning

confidence: 99%

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A detailed study of equatorial electrojet phenomenon using Ørsted satellite observations

Jadhav

Rajaram

2002

J. Geophys. Res.

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Detailed analysis of the scalar magnetic field data from Ørsted satellite for quiet days from April 1999 to March 2000 has been undertaken to study the equatorial electrojet (EEJ) phenomenon. An objective technique has been adopted for the identification of the EEJ from the satellite data and estimation of the standard parameters associated with it. EEJ strength computed using the satellite data and simultaneous ground magnetic observatory data, for the Indian and American sectors, correlate very well authenticating the method used. Estimated zonal variation in the EEJ parameters such as peak current intensity (J0), and total current (I+) are broadly consistent with the earlier observations. We, however, observe that the width of the EEJ varies considerably with longitude, a feature not seen in the Pogo data. The study shows that the EEJ axis (center of EEJ) closely follows the dip equator at altitude of 106 km, but there is a small departure that undergoes diurnal variation, with a minimum at noon. The globally averaged EEJ amplitude follows the expected diurnal pattern. Principal component analysis technique reveals that first four components can explain around two thirds of the electrojet variability. The first component, which contributes a little over 30% to the observed variance, could be identified with the global variation of the EEJ emanating from the day‐to‐day variability of the migrating tides. The second and fourth components, which account for around 15 and 10% of the variance, respectively, are driven by forcing that depends on whether the location of the EEJ in that sector is in the Northern or Southern Hemisphere. The third component provides maximum contributions wherever the geomagnetic and dip equators are sufficiently close, accounting for 12.5% of the variance. The remaining components could be associated with contribution of nonmigratory tides or other unknown mechanisms. Thus the present study suggests that besides conductivity, atmospheric tidal modes play important role in defining the zonal variability of the EEJ current system.

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Section: Comparison Between Satellite and Ground Observationssupporting

confidence: 88%

Section: Determination Of Eej Parametersmentioning

confidence: 99%

A detailed study of equatorial electrojet phenomenon using Ørsted satellite observations

Jadhav

Rajaram

2002

J. Geophys. Res.

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“…Except for the 30° separation bins, the significance of correlation is greater than 95%, implying that the estimation of the correlation coefficients is meaningful. The correlation coefficient in the central bin is 0.94 (significance ∼= 1.0) which is higher than the previous estimates for the Indian sector as 0.86 by Jadhav et al [2002] who used Ørsted and 0.9 by Yacob [1977] who used POGO data for a similar analysis. Agu and Onwumechili [1981] also report a correlation of 0.8 from POGO over the Indian region.…”

Section: Correlation Between Satellite and Ground Datacontrasting

confidence: 65%

“…Each observatory pair consists of one observatory close to the EEJ footprint and a second one outside of this area but both within the same longitude sector. The equatorial electrojet strength for an observatory pair is computed from the horizontal intensity, H, as Δ H EEJ − Δ H NonEEJ [see, e.g., Yacob , 1977; Alex and Mukherjee , 2001; Anderson et al , 2002], where Δ H is the variation of H from the mean midnight level for that observatory. Ideally, this differencing removes the core and large‐scale magnetospheric fields from the data, and on magnetically quiet days Δ H describes the daily variation of S q and EEJ plus their induced components.…”

Section: Observatory Datamentioning

confidence: 99%

“…There are very few reported attempts to estimate the longitudinal extent of the noontime equatorial electrojet. POGO satellite data were used by many authors to study the EEJ as well as to obtain its correlation with ground data [ Yacob , 1977; Agu and Onwumechili , 1981]. However, the studies were limited to finding the correlation coefficient and slope of the scatter for a large longitudinal window (20°, in most cases) above an observatory.…”

Section: Introductionmentioning

confidence: 99%

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Evidence for short spatial correlation lengths of the noontime equatorial electrojet inferred from a comparison of satellite and ground magnetic data

Manoj

Lühr

Maus³

et al. 2006

J. Geophys. Res.

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[1] The current density of the noontime equatorial electrojet (EEJ) as determined from CHAMP data is highly variable between successive passes of the satellite, which are separated by 23°in distance and 93 min in time. An open question is to which extent this variability is caused by temporal or spatial variations in the ionosphere. Another important question is the connection between EEJ and global solar-quiet (S q ) current systems. We try to answer these questions by comparing the EEJ current density estimated from highquality scalar magnetic field measurements of the CHAMP satellite with the magnetic horizontal intensity variations at six equatorial observatory pairs distributed across the globe. Data taken during the period 2000-2002 were used for the present study. We apply corrections for the effect of local time (LT) and S q fields. By estimating the correlation coefficients between the ground and satellite data as a function of distances between measurements, new insights into the spatial structure of the EEJ have been obtained. The high correlation, when CHAMP passes directly over an observatory, decays quickly in eastern and western directions. Typically, within ±15°of longitudinal separation between satellite and observatory, the correlation falls well below the statistical significance level. This observation holds for all longitude sectors. Interestingly, the correlation between CHAMP-inferred EEJ strength and observatory differences breaks down for the observatory pairs, outside of a ±4°latitudinal band. This implies that the EEJ and S q variations are uncorrelated for periods up to 1 hour. Additionally, it was found that monitoring of the EEJ can be performed best if the reference observatory is 4°to 5°apart from the dip equator.Citation: Manoj, C., H. Lühr, S. Maus, and N. Nagarajan (2006), Evidence for short spatial correlation lengths of the noontime equatorial electrojet inferred from a comparison of satellite and ground magnetic data,

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Indices of equatorial electrojet and counter-electrojet in the Indian region: Evolution of the indices and their authenticity

1983

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Indices of the equatorial electrojet and counter-electrojet in the Indian region have been evolved based on certain reasonable assumptions, by a criterion depending on the difference in the horizontal field strength between a station under the electrojet axis (Trivandrum) and a station outside the jet influence (Alibag). The indices enable one to characterize each day of the year by an appropriate index. Distribution, in the months, seasons and over the years, of the electrojet and counter-electrojet frequencies at Trivandrum during a 20-year period. 1959-78, is examined. The salient features oftbe distributions are: (i) Strong electro jets (range 50 nT) and the afternoon counter-electrojets occur, on an average, on about 50% of the days in the year; (ii) For the counter-electrojet, the mon:thly frequencies show an annual variation with a summer maximum, and for the strong electrojet, a semi-annual variation with maxima in the equinoxes: (iii) A secondary maximum is noted in January in the occurrence frequency of both counter-clectrojet and strong electrojet events; (iv) Intense electrojets occur with greater frequency in September.

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Internal induction by the equatorial electrojet in India examined with surface and satellite geomagnetic observations

Cited by 17 publications

References 10 publications

A detailed study of equatorial electrojet phenomenon using Ørsted satellite observations

A detailed study of equatorial electrojet phenomenon using Ørsted satellite observations

Evidence for short spatial correlation lengths of the noontime equatorial electrojet inferred from a comparison of satellite and ground magnetic data

Indices of equatorial electrojet and counter-electrojet in the Indian region: Evolution of the indices and their authenticity

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