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| Titel |
Antiparallel magnetic merging signatures during IMF BY>>0: longitudinal and latitudinal cusp aurora bifurcations |
| VerfasserIn |
S. Massetti |
| 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 ; 24, no. 8 ; Nr. 24, no. 8 (2006-09-13), S.2299-2311 |
| Datensatznummer |
250015628
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| Publikation (Nr.) |
 copernicus.org/angeo-24-2299-2006.pdf |
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| Zusammenfassung |
| A prominent dayside auroral event, occurred during an IMF BY-dominated
time interval, and characterized by the contemporaneous longitudinal and
latitudinal cusp bifurcations, is reported. The event was recorded the 19 December 2002,
between about 09:30–10:45 UT, by the ITACA2 twin auroral monitors
system, in the Greenland-Svalbard zone. The splitting of the ionospheric
footprint of the geomagnetic cusp, traced by the dayside auroral activity,
was recently identified with the signatures of antiparallel reconnection
episodes ongoing at different magnetopause locations, during large IMF
BY periods. The first part of the event showed a broad longitudinal
bifurcation of the red-dominated cusp aurora, displaced in the prenoon and
postnoon, with a separation up to ~1800 km, during northeast directed
IMF (clock-angle rotating from 45° to 90°). This observation widens
the range of IMF regimes that are known to drive a longitudinal bifurcation
of the cusp, since previous case-studies reported these events to occur
during southeast/southwest oriented IMF (clock-angle ≈135°).
The second part of the event, developed when the IMF turned to a nearly
horizontal orientation (BY>>0, BZ~0, clock-angle
~90°), and exhibited the simultaneous activation of the cusp
auroras in three distinct areas: i) two of them associated to the
above-mentioned longitudinally bifurcated cusp (~73°–75° CGM
latitude, type 1 cusp aurora), and linked to (near)antiparallel magnetic
reconnection patches equatorward the northern and the southern cusp, ii) the
other one characterized by isolated high-latitude (~76°–77°
CGM latitude, type 2 cusp aurora) rayed arc(s) with intense green emission, and
triggered by (near)antiparallel merging at the northern lobe (usually
observed during positive IMF BZ), poleward the local cusp. During this
phase, the longitudinal separation of the low-latitude type~1 cusp aurora was
about 1000 km wide, with a 500 km gap, while the latitudinal separation
between low- (type 1) and high-latitude (type 2) cusp auroras, in the postnoon, was
about 270–280 km at its maximum. The longitudinal gap, corresponding to a
zone with weak auroral emission, was found to likely map to the component
reconnection region at the subsolar magnetopause. The magnetic merging
topology that can be drawn on the basis of the reported cusp auroras support
the idea of a "mixed" merging scheme, with (near)antiparallel reconnection
at high-latitudes, and component reconnection in the subsolar region, as
recently proposed by other authors. |
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