Revisiting substorm events with preonset aurora
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Published:2018-10-19
Issue:5
Volume:36
Page:1419-1438
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ISSN:1432-0576
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Container-title:Annales Geophysicae
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language:en
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Short-container-title:Ann. Geophys.
Author:
Miyashita YukinagaORCID, Ieda Akimasa
Abstract
Abstract. Nishimura et al. (2010) proposed a new plasma intrusion or preonset aurora
scenario of substorm triggering. In this scenario, a substorm is triggered by
a fast earthward flow generated at the distant neutral line which corresponds
to a preonset auroral streamer or arc in the ionosphere propagating from the
auroral poleward boundary to the initial auroral brightening site, i.e.,
“preonset aurora”. In the present paper, we revisited three substorm events
reported as being triggered by such a mechanism related to preonset auroras,
based on THEMIS ground-based all-sky imager data. Unlike previous studies, we
examined the arrival timing of the preonset aurora relative to the three
steps of auroral onset arc development (initial brightening, enhancement of
the wave-like structure, and poleward expansion) to make the role of the
preonset aurora in the auroral steps clearer. Our detailed timing analysis
found that preonset auroral streamers reached the auroral onset arc but away
from the initial brightening site after initial brightening for two events,
while no preonset aurora reaching the initial brightening site could be
identified for the other event. This result suggests that the processes
associated with auroral streamers are unlikely to affect at least initial
brightening, even if we consider not only the presence and arrival timing and
location of the auroral streamers but also the scale of the corresponding
flow and flow vortices. We list a series of open questions for testing the
preonset aurora scenario further in future studies. Keywords. Magnetospheric physics (storms and substorms; auroral phenomena; magnetotail)
Publisher
Copernicus GmbH
Subject
Space and Planetary Science,Earth and Planetary Sciences (miscellaneous),Atmospheric Science,Geology,Astronomy and Astrophysics
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