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1

Electronic Resource

About the relationship between auroral electrojets and ring currents (2000)

Grafe, A. ; Feldstein, Y. I.

Springer

Annales geophysicae 18 (2000), S. 874-886

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ISSN: 0992-7689

Keywords: Magnetospheric physics (magnetosphere-ionosphere interactions; storms and substorms)

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract The relationship between the storm-time ring current and the auroral electrojets is investigated using IMAGE magnetometer data, DSt and H-SYM, and solar wind data. Statistical results as well as the investigation of single events show that the auroral electrojets occur also during nonstorm conditions without storm-time ring current development and even during the storm recovery phase of increasing DSt. A close correlation between electrojet intensity and ring current intensity was not found. Though the eastward electrojet moves equatorward during the storm main phase there is no unequivocal relationship between the movement of the westward electrojet and the ring current development. All these results suggest that the auroral electrojets and the ring current develop more or less independently of each other.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s00585-000-0874-4

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2

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Auroral electrojet dynamics during magnetic storms, connection with plasma precipitation and large-scale structure of the magnetospheric magnetic field (1999)

Feldstein, Y. I. ; Gromova, L. I. ; Grafe, A. ; [et al.]

Springer

Annales geophysicae 17 (1999), S. 497-507

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ISSN: 0992-7689

Keywords: Ionosphere (particle precipitation) ; Magnetospheric physics (current systems; magnetospheric configuration and dynamics)

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract Effect of the equatorward shift of the eastward and westward electrojets during magnetic storms main phase is analyzed based on the meridional chains of magnetic observatories EISCAT and IMAGE and several Russian observatories (geomagnetic longitude ≈110°, corrected geomagnetic latitudes 74°〉φ〉51°.) Magnetic storms of various Dst index intensity where the main phase falls on 1000 UT - 2400 UT interval were selected so that one of the observatory chains was located in the afternoon - near midnight sector of MLT. The eastward electrojet center shifts equatorward with Dst intensity increase: when Dst ≈ −50 nT the electrojet center is located at φ ≈ 62°, when Dst ≈ −300 nT it is placed at φ ≈ 54°. The westward electrojet center during magnetic storms main phase for intervals between substorms shifts equatorward with Dst increase: at φ ≈ 62° when Dst ≈ −100 nT and at φ ≈ 55° when Dst ≈ −300 nT. During substorms within the magnetic storms intervals the westward electrojet widens poleward covering latitudes φ ≈ 64°–65°. DMSP (F08, F10 and F11) satellite observations of auroral energy plasma precipitations at upper atmosphere altitudes were used to determine precipitation region structure and location of boundaries of various plasma domains during magnetic storms on May 10–11, 1992, February 5–7 and February 21–22, 1994. Interrelationships between center location, poleward and equatorward boundaries of electrojets and characteristic plasma regions are discussed. The electrojet center, poleward and equatorward boundaries along the magnetic observatories meridional chain were mapped to the magnetosphere using the geomagnetic field paraboloid model. The location of auroral energy oxygen ion regions in the night and evening magnetosphere is determined. Considerations are presented on the mechanism causing the appearance in the inner magnetosphere during active intervals of magnetic storms of ions with energy of tens KeV. In the framework of the magnetospheric magnetic field paraboloid model the influence of the ring current and magnetospheric tail plasma sheet currents on large-scale magnetosphere structure is considered.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s00585-999-0497-3

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3

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Ring current and auroral electrojets in connection with interplanetary medium parameters during magnetic storm (1994)

Feldstein, Y. I. ; Levitin, A. E. ; Golyshev, S. A. ; [et al.]

Springer

Annales geophysicae 12 (1994), S. 602-611

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ISSN: 0992-7689

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Notes: Abstract The relationship between the auroral electrojet indices (AE) and the ring current magnetic field (DR) was investigated by observations obtained during the magnetic storm on 1–3 April 1973. During the storm main phase the DR development is accompanied by a shift of the auroral electrojets toward the equator. As a result, the standard AE indices calculated on the basis of data from auroral observatories was substantially lower than the real values (AE’). To determine AE’ during the course of a storm main phase data from subauroral magnetic observatories should be used. It is shown that the intensity of the indices (AE’) which take into account the shift of the electrojets is increased substantially relative to the standard indices during the storm main phase. AE’ values are closely correlated with geoeffective solar wind parameters. A high correlation was obtained between AE’ and the energy flux into the ring current during the storm main phase. Analysis of magnetic field variations during intervals with intense southward IMF components demonstrates a decrease of the saturation effect of auroral electrojet currents if subauroral stations magnetic field variations are taken into account. This applies both to case studies and statistical data. The dynamics of the electrojets in connection with the development of the ring current and of magnetospheric substorms can be described by the presence (absence) of saturation for minimum (maximum) AE index values during a 1-h interval. The ring current magnetic field asymmetry (ASY) was calculated as the difference between the maximum and minimum field values along a parallel of latitude at low latitudes. The ASY value is closely correlated with geoeffective solar wind parameters and simultaneously is a more sensitive indicator of IMF Bz variations than the symmetric ring current. ASY increases (decreases) faster during the main phase (the recovery phase) than DR. The magnetic field decay at low latitudes in the recovery phase occurs faster in the afternoon sector than at dusk.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s00585-994-0602-6

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4

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Comment on ‘Magnetospheric source region of discrete auroras inferred from their relationship with isotropy boundaries of energetic particles’ by A. G. Yahnin et al. (1998)

Feldstein, Y. I. ; Galperin, Y. I.

Springer

Annales geophysicae 17 (1998), S. 37-41

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ISSN: 0992-7689

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Physics

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/s00585-999-0037-1

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5

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Geomagnetic activity and the high latitude magnetic field of the Sun (1979)

LIVSHITS, M. A. ; VALCHUK, T. E. ; FELDSTEIN, Y. I.

[s.l.] : Nature Publishing Group

Nature 278 (1979), S. 241-243

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ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] From measurements by the Mount Wilson7'8, Cambridge9 and Crimea10 magnetographs one finds that the general magnetic field of the Sun varies with a period of -22 yr. Then assuming the first year of the 11-yr cycle and the even numbered years as the beginning of each oscillation and taking the 22-yr ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/278241a0

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6

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Modelling of the magnetic field of magnetospheric ring current as a function of interplanetary medium parameters (1992)

Feldstein, Y. I.

Springer

Space science reviews 59 (1992), S. 83-165

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ISSN: 1572-9672

Source: Springer Online Journal Archives 1860-2000

Topics: Physics

Notes: Abstract The models are examined which are proposed elsewhere for describing the magnetic field dynamics in ring-currentDR during magnetic storms on the basis of the magnetospheric energy balance equation. The equation parameters, the functions of injectionF and decay τ, are assumed to depend on interplanetary medium parameters (F and τ during the storm main phase) and on ring-current intensity (τ during the recovery phase). The present-day models are shown to be able of describing theDR variations to within a good accuracy (the r.m.s. deviation 5 〈δ 〈 15 nT, the correlation coefficient 0.85 〈r 〈 1). The models describe a fraction of the geomagnetic field variation during a magnetic storm controlled by the geoeffective characteristic of interplanetary medium and, therefore responds directly to the variation of the latter. The fraction forms the basis of the geomagnetic field variations in low and middle latitudes. The shorter-term variations ofDR are affected by the injections into the inner magnetosphere during substorm intervals. During magnetic storms, the auroral electrojets shift to subauroral latitudes. When determining theAE indices, the data from the auroral-zone stations must be supplemented with the data from subauroral observatories. Otherwise, erratic conclusions may be obtained concerning the character of the relationships ofDR toAE or ofAE to interplanetary medium parameters. Considering this circumstance, the auroral electrojet intensity during the main phase is closely related to the energy flux supplied to the ring current. It is this fact that gives rise simultaneously to the intensification of auroral electrojets and to the large-scale decrease of magnetic field in low latitudes. The longitudinal asymmetry of magnetic field on the Earth's surface is closely associated with the geoeffective parameters of interplanetary medium, thereby making it possible to model-estimate the magnetic field variations during magnetic storms at given observatories. The inclusion of the field asymmetry due to the system of large-scale currents improves significantly the agreement between the predicted and model field variations at subauroral and midlatitude observatories. The first harmonic amplitude of field variation increases with decreasing latitude. This means that the long-period component of theD st -variation asymmetry is due rather to the ring-current asymmetry, while the shorter-term fluctuations are produced by electrojets. The asymmetry correlates better with theAL indices (westward electrojet) than with theAU indices (eastward electrojet). The total ion energy in the inner magnetosphere during the storm main phase is sufficient for the magnetic field observed on the Earth's surface to be generated. The energy flux to the ring current is ∼ 15% of the ɛ-energy flux into the magnetosphere.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01262538

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