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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 36, issue 5 | Copyright
Ann. Geophys., 36, 1419-1438, 2018
https://doi.org/10.5194/angeo-36-1419-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Regular paper 19 Oct 2018

Regular paper | 19 Oct 2018

Revisiting substorm events with preonset aurora

Yukinaga Miyashita1 and Akimasa Ieda2 Yukinaga Miyashita and Akimasa Ieda
  • 1Korea Astronomy and Space Science Institute, Daejeon, South Korea
  • 2Institute for Space-Earth Environmental Research, Nagoya University, Nagoya, Japan

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.

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A new plasma intrusion or preonset aurora scenario of substorm triggering proposed by Nishimura et al. (2010) needs to be tested. To test the scenario, we revisited three of their substorm events in detail, based on THEMIS ground-based all-sky imager data. We list a series of open questions for testing the scenario further in future studies.
A new plasma intrusion or preonset aurora scenario of substorm triggering proposed by Nishimura...
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