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| Titel |
Substorms and polar cap convection: the 10 January 2004 interplanetary CME case |
| VerfasserIn |
Y. Andalsvik, P. E. Sandholt, C. J. Farrugia |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 30, no. 1 ; Nr. 30, no. 1 (2012-01-06), S.67-80 |
| Datensatznummer |
250017164
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| Publikation (Nr.) |
 copernicus.org/angeo-30-67-2012.pdf |
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| Zusammenfassung |
| The expansion-contraction model of
Dungey cell plasma convection has two different convection
sources, i.e. reconnections at the magnetopause
and in the magnetotail. The spatial-temporal structure of the
nightside source is not yet well understood.
In this study we shall identify temporal variations
in the winter polar cap convection structure during substorm activity
under steady interplanetary conditions.
Substorm activity (electrojets and particle precipitations)
is monitored by
excellent ground-satellite DMSP F15 conjunctions in the
dusk-premidnight sector. We take advantage of the wide latitudinal
coverage of the IMAGE chain of ground magnetometers in
Svalbard – Scandinavia – Russia for the purpose of
monitoring magnetic deflections
associated with polar cap convection and substorm electrojets.
These are augmented by
direct observations of
polar cap convection derived from SuperDARN radars and
cross-track ion drift observations during
traversals of polar cap along the
dusk-dawn meridian by spacecraft DMSP F13.
The interval we study is characterized by
moderate, stable forcing of the
magnetosphere-ionosphere system
(EKL = 4.0–4.5 mV m−1; cross polar cap potential (CPCP),
Φ (Boyle) = 115 kV)
during Earth passage of an
interplanetary CME (ICME), choosing an 4-h interval where
the magnetic field pointed continuously
south-west (Bz < 0; By < 0).
The combination of
continuous monitoring of ground magnetic deflections and
the F13 cross-track ion drift
observations in the polar cap allows us to infer the temporal
CPCP structure on time scales less than the ~10 min
duration of
F13 polar cap transits.
We arrived at the following estimates of the
dayside and nightside contributions to the CPCP
(CPCP = CPCP/day + CPCP/night)
under two intervals of substorm activity:
CPCP/day ~110 kV; CPCP/night ~50 kV (45% CPCP
increase during substorms).
The temporal CPCP structure during one of the substorm cases
resulted in a dawn-dusk convection asymmetry
measured by DMSP F13 which is
opposite to that expected from the prevailing
negative By polarity of the ICME magnetic field,
a clear indication of a nightside source. |
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