Other
Scientific paper
Dec 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agufmsm12b..09l&link_type=abstract
American Geophysical Union, Fall Meeting 2001, abstract #SM12B-09
Other
2407 Auroral Ionosphere (2704), 2704 Auroral Phenomena (2407), 2788 Storms And Substorms
Scientific paper
High-resolution CANOPUS meridian-scanning photometer and all-sky imager observations of pre-onset and expansion-phase auroral arcs are analyzed for onsets that evolve into full substorms and those which evolve into pseudo-breakups. Pseudo-breakups are defined here to be those for which expansion-phase auroral activity does not extend poleward as far as the poleward boundary of the auroral zone. Our analysis shows no other features that distinguish onsets that evolve into full substorms from those that evolve into pseudo-breakups. Typically, one or more relatively broad arcs are seen across the sky throughout the growth phase prior to onset. Break-up at onset, however, does not occur along one of these arcs. Instead it occurs along a noticeably thinner arc that forms a few minutes prior to breakup near the equatorward border of the auroral oval. This intensity of this breakup arc increases in intensity quasi-linearly for the few minutes prior to the time normally identified as substorm onset, and then increases dramatically. Arcs poleward of the arc that breaks up appear to be unaffected by substorm onset until expansion-phase auroral activity moves poleward to the location of such arcs. Arcs poleward of the poleward-most extent of pseudo-breakup auroral activity show no affects of a pseudo-breakup. These observations imply that an expansion-phase does not significantly affect the plasma sheet in regions anti-sunward of the field lines having expansion-phase auroral activity until expansion phase activity moves poleward to those regions. For pseudo breakups, the observations imply that expansion phase activity never significantly affects plasma sheet regions anti-sunward of the poleward-most extent of field lines having auroral activity. Since some pseudo-breakups extend only a small distance poleward of their onset location, and the onset of full substorms and of pseudo-breakups appear to be indistinguishable, our observations imply that plasma sheet regions beyond the inner plasma sheet region where breakup initiates do not play a significant role in expansion-phase onset.
Donovan Eric F.
Lyons Larry R.
Voronkov Igor
Zesta Eftyhia
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