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| Titel |
EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary |
| VerfasserIn |
A. T. Aikio, T. Pitkänen, D. Fontaine, I. Dandouras, O. Amm, A. Kozlovsky, A. Vaivdas, A. Fazakerley |
| 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 ; 26, no. 1 ; Nr. 26, no. 1 (2008-02-04), S.87-105 |
| Datensatznummer |
250016005
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| Publikation (Nr.) |
 copernicus.org/angeo-26-87-2008.pdf |
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| Zusammenfassung |
The dynamics of the polar cap boundary and auroral oval in the nightside
ionosphere are studied during late expansion and recovery of a substorm from
the region between Tromsø (66.6° cgmLat) and Longyearbyen
(75.2° cgmLat) on 27 February 2004 by using the coordinated EISCAT
incoherent scatter radar, MIRACLE magnetometer and Cluster satellite
measurements. During the late substorm expansion/early recovery phase, the
polar cap boundary (PCB) made zig-zag-type motion with amplitude of
2.5° cgmLat and period of about 30 min near magnetic midnight. We
suggest that the poleward motions of the PCB were produced by bursts of
enhanced reconnection at the near-Earth neutral line (NENL). The subsequent
equatorward motions of the PCB would then represent the recovery of the
merging line towards the equilibrium state (Cowley and Lockwood, 1992). The
observed bursts of enhanced westward electrojet just equatorward of the polar
cap boundary during poleward expansions were produced plausibly by particles
accelerated in the vicinity of the neutral line and thus lend evidence to the
Cowley-Lockwood paradigm.
During the substorm recovery phase, the footpoints of the Cluster satellites
at a geocentric distance of 4.4 RE mapped in the vicinity of EISCAT
measurements. Cluster data indicate that outflow of H+ and O+ ions took
place within the plasma sheet boundary layer (PSBL) as noted in some earlier
studies as well. We show that in this case the PSBL corresponded to a region
of enhanced electron temperature in the ionospheric F region. It is suggested
that the ion outflow originates from the F region as a result of increased
ambipolar diffusion. At higher altitudes, the ions could be further energized
by waves, which at Cluster altitudes were observed as BBELF (broad band extra
low frequency) fluctuations.
The four-satellite configuration of Cluster revealed a sudden poleward
expansion of the PSBL by 2° during ~5 min. The beginning of the
poleward motion of the PCB was associated with an intensification of the
downward FAC at the boundary. We suggest that the downward FAC sheet at the
PCB is the high-altitude counterpart of the Earthward flowing FAC produced in
the vicinity of the magnetotail neutral line by the Hall effect (Sonnerup, 1979)
during a short-lived reconnection pulse. |
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