The influence of geomagnetic activity on the radial variation of the magnetospheric electric field between <i>L</i>=4 and 10

Kaye, S. M.; Kivelson, M. G.

doi:10.1029/ja086ia02p00863

Cited by 23 publications

(10 citation statements)

References 22 publications

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“…Although the standard error is large, the average value of γ is smaller with southward IMF. This is consistent with the result of Kaye and Kivelson [1981], indicating a tendency of weaker shielding as the activity increases. We note that activity is stronger with southward IMF.…”

Section: Discussionsupporting

confidence: 92%

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Electric field measurements in the inner magnetosphere by Cluster EDI

et al. 2003

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[1] We report electric field measurements in the inner magnetosphere from the Electron Drift Instrument (EDI) on Cluster at distances of 4 < L < 10. The data used in this study span more than 1 year so that all local times are covered. Both components of the electric field perpendicular to the ambient magnetic field are mapped into the equatorial plane with the magnetic field model of Tsyganenko and Stern [1996]. Average values and standard deviations are sorted by the polarity of the B Z component of the interplanetary magnetic field (IMF). Average Kp values for both B Z polarities are 1.45 (B Z > 0) and 2.45 (B Z < 0). These electric fields are discussed in terms of their sources such as the ionospheric dynamo and the solar wind-magnetosphere interaction. We also quantify the electric field as follows: the average shielding parameter g [Volland, 1973;Stern, 1975] is $2, although the value for southward IMF is smaller than the value for northward IMF. The parameter g is larger on the duskside than in the dawn sector. The average rate of sunward transport of magnetic flux, equivalent to the duskward electric field, is estimated as 0.32 mV/m for southward IMF. Finally, fluctuations tend to be larger than the DC component around the stagnation point, which could lead to outflow of plasmaspheric material.

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Section: Discussionsupporting

confidence: 92%

“… Baumjohann and Haerendel [1985] estimated γ as 2 by using the ratio of radial to azimuthal components at geosynchronous orbit. On the other hand, Kaye and Kivelson [1981] determined γ by using dependence of the electric field on L value as follows. The parameter γ varies inversely with Kp for Kp ≲ 3, and γ ∼ 1 for Kp ≲ 3.…”

Section: Discussionmentioning

confidence: 99%

Electric field measurements in the inner magnetosphere by Cluster EDI

et al. 2003

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“…The latter depends in the ¾olland-Stern model (Volland [1973] and Stern [1975]; cfi also paper 1) • = -5 fi• sin qb (3) especially on the shaping or shielding factor 7 (• denotes the electric potential at radial distance r and azimuth qb, A• is the cross-tail or cross-polar-cap potential difference, and Ay is half the distance between the dawn and dusk magnetopause). Since 7 varies with magnetic activity between roughly 1 and 3 [Kaye and Kivelson, 1981], we cannot expect the correlation between…”

Section: Dayside Mergingmentioning

confidence: 98%

Magnetospheric convection observed between 0600 and 2100 LT: Solar wind and IMF dependence

Baumjohann¹,

Haerendel²

1985

J. Geophys. Res.

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Using data from the GEOS 2 electron gun experiment, we have analyzed the dependence of the dayside convection electric field at L = 6.6 (averaged into 3‐hour LT bins) on solar wind and interplanetary magnetic field conditions. The convection electric field does not correlate at all with the solar wind momentum flux density (correlation coefficients of <0.25). Hence viscous interaction plays only a minor role for equatorial magnetospheric convection at L = 6.6. The correlation coefficients for convection electric field versus merging electric field are of the order of 0.5–0.6, thus indicating that dayside convection is predominantly driven by dayside merging. The regression coefficients, describing the (LT‐dependent) transfer of the merging electric field to synchronous orbit, are of the order of 0.1–0.2. Their LT dependence follows approximately that described by a Volland‐Stern model with γ = 2, except that the regression analysis yields a dawn‐dusk asymmetry with the dusk sector electric fields being about twice as strong as those in the dawn sector. For the above shielding factor (γ = 2) the regression coefficients are consistent with a merging efficiency of about 20%. The regression constants (of the order of 0.05 mV/m) apparently describe an electric field stemming from the ionospheric wind dynamo. A comparison of the electric field described by the regression constants and two empirical models of quiet day electric fields implies that these models still include a substantial dawn‐to‐dusk electric field, thus indicating the presence of solar wind dynamo action even during quiet intervals.

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“…Ejiri et al [1978] derived an analytic expression for the zero-energy Affv6n boundary under nonuniform electric field situations that uses a shaping factor ¾. Recently, Kaye and Kivelson [1981] suggested that the value of ¾ reflects the degree to which space charges shield the convective electric field from the inner magnetosphere. The case ¾ = 1 corresponds to situations of uniform dawn to dusk fields in which there is no shielding.…”

Section: A Quasi-empirical Representation Of the Observed Boundariesmentioning

confidence: 99%

DMSP/F2 electron observations of equatorward auroral boundaries and their relationship to magnetospheric electric fields

Gussenhoven¹,

Hardy²,

Burke³

1981

J. Geophys. Res.

142

105

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Energetic electron measurements from a particle detector on the DMSP/F2 satellite have been used to determine the corrected geomagnetic latitude ΛCGM of the equatorward boundary of the auroral oval. The satellite was launched into a nearly sun‐synchronous, polar orbit centered on the 0700–1900 MLT meridian. Because of the wobble of the dipole and a very slow precessional motion of the orbit more than 6000 boundary crossings could be studied in the 1600–2300 and 0400–1000 MLT sectors. The detectors, which have large geometric factors, look radially away from the earth and detect precipitating electrons with energies between 50 eV and 20 keV. In the evening sector the equatorward boundaries are precisely determined from the rise in the total electron flux. The morningside boundary cannot always be clearly delineated. Data were divided into 1‐hour magnetic local time bins with ∼400 samples per bin. In each of the MLT bins, ΛCGM was found to be linearly correlated to the KP index. Regression values of ΛCGM were projected to the magnetic equatorial plane by using the Mead‐Fairfield magnetic field model. The projected boundaries are not in good agreement with the injection boundaries of Mauk and McIlwain (1974). They are best fit to boundaries derived by using Volland‐Stern type electric fields with the axis of symmetry rotated into the evening sector for KP <2 and into the afternoon sector for KP ≥2.

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The influence of geomagnetic activity on the radial variation of the magnetospheric electric field between L=4 and 10

Cited by 23 publications

References 22 publications

Electric field measurements in the inner magnetosphere by Cluster EDI

Electric field measurements in the inner magnetosphere by Cluster EDI

Magnetospheric convection observed between 0600 and 2100 LT: Solar wind and IMF dependence

DMSP/F2 electron observations of equatorward auroral boundaries and their relationship to magnetospheric electric fields

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