Magnetospheric electric fields and currents

Mauk, B. H.; Zanetti, L. J.

doi:10.1029/rg025i003p00541

Cited by 55 publications

(30 citation statements)

References 255 publications

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“…It is a region characterized by an exponential decrease of electron energy density with decreasing radial distance and is generally located at geocentric distances of ~6 to 8 RE in the nightside. It is implicitly assumed by a number of researchers that the inner edge of the plasma sheet is associated with an earthward decrease of the total plasma pressure and theories on the closure of the large scale region 2 field-aligned current system [lijima and Potemra, 1978] have been built upon this assumption (see, e.g., the review by Mauk and Zanetti, 1987). As pointed out by Mauk and Zanetti [1987], the observed plasma pressure shows a persistent earthward increase rather than a decrease in the geocentric distances usually ascribed to be the inner edge of the plasma sheet.…”

Section: Summary and Discussionmentioning

confidence: 99%

Empirical modeling of the quiet time nightside magnetosphere

Lui¹,

Spence²,

Stern³

1994

J. Geophys. Res.

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Empirical modeling of plasma pressure and magnetic field for the quiet time nightside magnetosphere is investigated. Two models are constructed for this study. One model, referred to here as T89R, is basically the magnetic field model of Tsyganenko [1989] but is modified by the addition of an inner eastward ring current at a radial distance of ~3 RE as suggested by observation. The other is a combination of the T89R model and the long version of the magnetic field model of Tsyganenko [1987] such that the former dominates the magnetic field in the inner magnetosphere while the latter prevails in the distant tail. The distribution of plasma pressure which is required to balance the magnetic force for each of these two field models is computed along the tail axis in the midnight meridian. The occurrence of pressure anisotropy in the inner magnetospheric region is also taken into account by determining an empirical fit to the observed plasma pressure anisotropy. This represents the first effort to obtain the plasma pressure distribution in force equilibrium with magnetic stresses from an empirical field model with the inclusion of pressure anisotropy. The inclusion of pressure anisotropy alters the plasma pressure by as much as a factor of -3 in the inner magnetosphere. The deduced plasma pressure profile along the tail axis is found to be in good agreement with the observed quiet time plasma pressure for geocentric distances between ~2 and ~35 RE-

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Section: Summary and Discussionmentioning

confidence: 99%

Empirical modeling of the quiet time nightside magnetosphere

Lui¹,

Spence²,

Stern³

1994

J. Geophys. Res.

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“…When the periods are hours rather than days, the spectrum is dominated by more localized ionospheric and magnetospheric sources, including high-latitude ionospheric substorm currents, field-aligned currents and partial ring currents (Mauk & Zanetti 1987). Great strides have been made during the last 10 years in generating 3-D current models which match the magnetic fields observed on the ground (Kamide & Richmond 1984).…”

Section: Sources Of T H E Electromagnetic Spectrummentioning

confidence: 99%

Global induction and the spatial structure of mid-latitude geomagnetic variations

Banks

Ainsworth

1992

Geophysical Journal International

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SUMMARY A pre‐requisite for more precise estimates of the electromagnetic response of the Earth is a better knowledge of the origin and spatial structure of geomagnetic time variations with periods of a few hours to several years. The period range from four hours to four days is particularly crucial for constraining upper mantle conductivity models, but is difficult to analyse because of overlapping contributions from current systems with different spatial scales. A period band centred on two days has been isolated from two years of hourly mean values recorded at up to 130 observatories. Plots of the coherence between pairs of records of the same component of the field at different observatories, as a function of the station separation, prove to be a valuable diagnostic tool. They show that two groups of sources contribute to this part of the spectrum. One group has a spatial scale in excess of 10 000 km, dominates the geomagnetic north (Xm) component, but produces no east (Ym) component. It can be satisfactorily modelled by a P01 spherical harmonic, and must be generated by fluctuations in the symmetric magnetospheric ring current. The spatial coherence of the second group falls to zero in a distance of 5000–7000 km, and can be predicted by a stochastic source model for which the autocovariance scale length is 7000 km. The spatial structure of the two groups is further investigated using the principal component technique of Egbert & Booker (1989). The spectrum is dominated by the largest eigenvalue, and the eigenfunctions corresponding to this mode show the expected P01 source behaviour. The modes which correspond to the next largest eigenvalues are organized into foci approximately 10 000 km across. The vertical fields associated with these modes are of low amplitude at mid‐latitudes, but increase steeply beyond 50d̀. Estimates of the P01 response based upon the horizontal and vertical fields recorded at a single station will be biased by the contribution from the higher order modes. The magnetic observatory network is incapable of describing them properly on a global basis, and only the European subarray is sufficiently dense to form locally valid response estimates.

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“…Nightside FACs, embedded in the auroral oval, are intimately related to both the tail current and the ring current (Mauk and Zanetti, 1987). Therefore, we expect that the solar wind will have a different effect on the dayside and nightside FACs' intensities and locations during intense storms.…”

Section: Introductionmentioning

confidence: 99%

Field-aligned currents observed by CHAMP during the intense 2003 geomagnetic storm events

Wang

Lühr

et al. 2006

Ann. Geophys.

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Abstract. This study concentrates on the characteristics of field-aligned currents (FACs) in both hemispheres during the extreme storms in October and November 2003. Highresolution CHAMP magnetic data reflect the dynamics of FACs during these geomagnetic storms, which are different from normal periods. The peak intensity and most equatorward location of FACs in response to the storm phases are examined separately for both hemispheres, as well as for the dayside and nightside. The corresponding large-scale FAC peak densities are, on average, enhanced by about a factor of 5 compared to the quiet-time FACs' strengths. And the FAC densities on the dayside are, on average, 2.5 times larger in the Southern (summer) than in the Northern (winter) Hemisphere, while the observed intensities on the nightside are comparable between the two hemispheres. Solar wind dynamic pressure is correlated with the FACs strength on the dayside. However, the latitudinal variations of the FACs are compared with the variations in D st and the interplanetary magnetic field component B z , in order to determine how these parameters control the large-scale FACs' configuration in the polar region. We have determined that (1) the equatorward shift of FACs on the dayside is directly controlled by the southward IMF B z and there is a saturation of the latitudinal displacement for large value of negative B z . In the winter hemisphere this saturation occurs at higher latitudes than in the summer hemisphere. (2) The equatorward expansion of the nightside FACs is delayed with respect to the solar wind input. The poleward recovery of FACs on the nightside is slower than on the dayside. The latitudinal variations on the nightside are better described by the variations of the D st index. (3) The latitudinal width of the FAC region on the nightside spreads over a wide range of about 25 • in latitude.

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Magnetospheric electric fields and currents

Cited by 55 publications

References 255 publications

Empirical modeling of the quiet time nightside magnetosphere

Empirical modeling of the quiet time nightside magnetosphere

Global induction and the spatial structure of mid-latitude geomagnetic variations

Field-aligned currents observed by CHAMP during the intense 2003 geomagnetic storm events

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