Antiparallel magnetic merging signatures during IMF B Y >>0: longitudinal and latitudinal cusp aurora bifurcations
A prominent dayside auroral event, occurred during an IMF B Y -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 ITACA 2 twin auroral monitor...
| Published in: | Annales Geophysicae |
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| Main Author: | |
| Format: | Article in Journal/Newspaper |
| Language: | English |
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Copernicus Publications
2006
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| Subjects: | |
| Online Access: | https://doi.org/10.5194/angeo-24-2299-2006 https://doaj.org/article/90d24792d65a4069946ac2da7f921add |
| Summary: | A prominent dayside auroral event, occurred during an IMF B Y -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 ITACA 2 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 B Y 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 ( B Y >>0, B Z ~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 B Z ), 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 ... |
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