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JOURNAL OF GEOPHYSICAL RESEARCH,
VOL. 112,
A10304,
doi:10.1029/2007JA012376,
2007
Equatorial Ionospheric Electric Fields During the November 2004 Magnetic Storm
B. G. Fejer
Center for Atmospheric and Space Science, Utah State University, Logan, Utah, USA
J. W. Jensen
Center for Atmospheric and Space Science, Utah State University, Logan, Utah, USA
T. Kikuchi
Solar Terrestrial Environment Laboratory, Nagoya University, Nagoya, Aichi, Japan
M. A. Abdu
Instituto de Pesquisas Espaciais, Sao Paulo, Brazil
J. L. Chau
Radio Observatorio de Jicamarca, Instituto Geofisico del Peru, Peru
Abstract
We use radar measurements from the Jicamarca Radio Observatory, magnetometer observations from the Pacific sector and ionosonde
data from Brazil to study equatorial ionospheric electric fields during the November 2004 geomagnetic storm. Our data show
very large eastward and westward daytime electrojet current perturbations with lifetimes of about an hour (indicative of undershielding
and overshielding prompt penetration electric fields) in the Pacific equatorial region during the November 7 main phase of
the storm, when the southward IMF, the solar wind and reconnection electric fields, and the polar cap potential drops had
very large and nearly steady values. This result is inconsistent with the recent suggestion that solar wind electric fields
penetrate without attenuation into the equatorial ionosphere for several hours during storm main phase. The largest daytime
prompt penetration electric fields (about 3 mV/m) ever observed over Jicamarca occurred during the November 9 storm main phase,
when large equatorial electrojet current and drift perturbations were also present in the Pacific and Brazilian equatorial
regions. The rise and decay times of these equatorial electric fields were about 20 min longer than of the corresponding solar
wind electric fields. The ratios of prompt penetration electric fields and corresponding solar wind electric field changes
were highly variable even during the day, and had largest values near dawn. Also, the prompt penetration electric fields did
not show polar cap potential drop saturation effects. Our results clearly highlight that the relationships of prompt penetration
and solar wind electric fields, and polar cap potentials are far more complex than implied by simple proportionality factors.
Received 27
February
2007;
accepted 10
August
2007;
published 16
October
2007.
Keywords: Disturbance electric fields;
ionospheric storm effects;
ionos plasma drifts.
Index Terms: 2411 Ionosphere: Electric fields (2712); 2415 Ionosphere: Equatorial ionosphere; 2435 Ionosphere: Ionospheric disturbances; 2431 Ionosphere: Ionosphere/magnetosphere interactions (2736).
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Citation: Fejer, B. G., J. W. Jensen, T. Kikuchi, M. A. Abdu, and J. L. Chau
(2007),
Equatorial Ionospheric Electric Fields During the November 2004 Magnetic Storm,
J. Geophys. Res.,
112,
A10304,
doi:10.1029/2007JA012376.
Copyright 2007 by the American Geophysical Union.
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