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| Titel |
Ionospheric flow during extended intervals of northward but By -dominated IMF |
| VerfasserIn |
A. Grocott, S. W. H. Cowley, J. B. Sigwarth |
| 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 ; 21, no. 2 ; Nr. 21, no. 2, S.509-538 |
| Datensatznummer |
250014572
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| Publikation (Nr.) |
 copernicus.org/angeo-21-509-2003.pdf |
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| Zusammenfassung |
We present SuperDARN
radar observations of the nightside high-latitude ionospheric flow during two
6-hour intervals of quasi-steady northward interplanetary magnetic field (IMF).
During both intervals (01:30–07:30 UT on 2 December and 21:00–03:00 UT on
14/15 December 1999), the solar wind and IMF remained relatively steady with Bz
positive and By negative, such that the IMF clock angle was ~ - 50° to - 60°.
Throughout both intervals the radar data clearly indicate the presence of a
highly distorted By-dominated twin cell flow pattern, indicative of an open
magnetosphere, which is confirmed by DMSP and auroral data. Estimates of the
changes in open flux present during each interval indicate approximately
balanced dayside and nightside reconnection at rates of ~ 30–35 kV over the
full 6 h. However, strong bursts of flow with speeds of over ~ 1000 ms-1
are observed near magnetic midnight on time scales of ~ 1 h, which are
associated with increases in the transpolar voltage. These are indicative of
the net closure of open flux by recon-nection in the tail. During one large
flow burst, the night-side reconnection rate is estimated to have been ~ 1.5
times the dayside rate, i.e. ~ 45–60 kV compared with ~ 30–40 kV. Magnetic
bays, which would indicate the formation of a sub-storm current wedge, are not
observed in association with these bursts. In addition, no low-latitude Pi2s or
geostationary particle injections were observed, although some local, small
amplitude Pi2-band (5–50 mHz) activity does accompany the bursts. Coincident
measurements of the flow and of the low amplitude magnetic perturbations reveal
nightside ionospheric conductances of no more than a few mho, indicative of
little associated precipitation. Therefore, we suggest that the flow bursts are
the ionospheric manifestation of bursty reconnection events occurring in the
more distant geomagnetic tail. The main implication of these findings is that,
under the circumstances examined here, the convection cycle is not equivalent
to the usual substorm cycle that occurs for southward IMF.
Key words. Ionosphere (plasma
convection; ionosphere-magnetosphere interactions) – Magnetospheric Physics (magnetotail) |
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