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Ann. Geophys., 24, 2243-2276, 2006
www.ann-geophys.net/24/2243/2006/
© European Geosciences Union 2006
Auroral electrojets and boundaries of plasma domains in the magnetosphere during magnetically disturbed intervals
Y. I. Feldstein1, V. A. Popov1, J. A. Cumnock2, A. Prigancova3, L. G. Blomberg2, J. U. Kozyra4, B. T. Tsurutani5, L. I. Gromova1, and A. E. Levitin1
1Institute of Terrestrial Magnetism, Ionosphere and Radio Wave Propagation, Troitsk, Moscow Region, Russia
2Alfvén Laboratory, Royal Institute of Technology, Stockholm, Sweden
3Geophysical Institute, Slovak Academy of Sciences, Bratislava, Slovakia
4Space Physics Research Laboratory, University of Michigan, Ann Arbor, MI, USA
5Jet Propulsion Laboratory, Pasadena, CA, USA
Abstract. We investigate variations in the location and intensity
of the auroral electrojets during magnetic storms and substorms using a
numerical method for estimating the equivalent ionospheric currents based on
data from meridian chains of magnetic observatories. Special attention was
paid to the complex structure of the electrojets and their interrelationship
with diffuse and discrete particle precipitation and field-aligned currents
in the dusk sector. During magnetospheric substorms the eastward electrojet
(EE) location in the evening sector changes with local time from cusp
latitudes (Φ~77°) during early afternoon to latitudes of diffuse
auroral precipitation (Φ~65°) equatorward of the auroral oval
before midnight. During the main phase of an intense magnetic storm the
eastward currents in the noon-early evening sector adjoin to the cusp at
Φ~65° and in the pre-midnight sector are located at
subauroral latitude Φ~57°. The westward
electrojet (WE) is located along the auroral oval from evening through night
to the morning sector and adjoins to the polar electrojet (PE) located
at cusp latitudes in the dayside sector. The integrated values of the
eastward (westward) equivalent ionospheric current during the intense
substorm are ~0.5 MA (~1.5 MA), whereas they are 0.7 MA (3.0 MA)
during the storm main phase maximum. The latitudes of
auroral particle precipitation in the dusk sector are identical with those
of both electrojets. The EE in the evening sector is accompanied by particle
precipitation mainly from the Alfvén layer but also from the near-Earth
part of the central plasma sheet. In the lower-latitude part of the EE the
field-aligned currents (FACs) flow into the ionosphere (Region 2 FAC), and at
its higher-latitude part the FACs flow out of the ionosphere (Region 1 FAC).
During intense disturbances, in addition to the Region 2 FAC and the Region
1 FAC, a Region 3 FAC with the downward current was identified.
This FAC is accompanied by diffuse electron precipitation from
the plasma sheet boundary layer. Actually, the triple
system of FAC is observed in the evening sector and, as a consequence, the WE
and the EE overlap. The WE in the evening sector comprises only the
high-latitude periphery of the plasma precipitation region and corresponds
to the Hall current between the Region 1 FAC and Region 3 FAC. During the
September 1998 magnetic storm, two velocity bursts (~2–4 km/s)
in the magnetospheric convection were observed at the latitudes
of particle precipitation from the central plasma sheet and at
subauroral latitudes near the ionospheric trough. These kind of bursts are
known as subauroral polarization streams (SAPS). In the evening sector the
Alfvén layer equatorial boundary for precipitating ions is located more
equatorward than that for electrons. This may favour northward electric
field generation between these boundaries and may cause high speed westward
ions drift visualized as SAPS. Meanwhile, high speed ion drifts cover a
wider range of latitudes than the distance between the equatorward
boundaries of ions and electrons precipitation. To summarize the results
obtained a new scheme of 3-D currents in the magnetosphere-ionosphere system
and a clarified view of interrelated 3-D currents and magnetospheric plasma
domains are proposed.
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