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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Discussion papers
https://doi.org/10.5194/angeo-2019-118
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/angeo-2019-118
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: regular paper 25 Sep 2019

Submitted as: regular paper | 25 Sep 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Annales Geophysicae (ANGEO).

Polar substorm on 7 December 2015: pre-onset phenomena and features of auroral breakup

Vladimir V. Safargaleev1, Alexander E. Kozlovsky2, and Valery M. Mitrofanov1 Vladimir V. Safargaleev et al.
  • 1Polar Geophysical Institute, Apatity, Russia
  • 2Sodankylä Geophysical Observatory, Sodankylä, Finland

Abstract. Comprehensive analysis of a moderate 600-nT substorm was performed with using simultaneous optical observations inside the auroral oval and in the polar cap, combined with data from satellites, radars, and ground magnetometers. The onset took place near the poleward boundary of the auroral oval that is not typical for classical substorms. The substorm onset was preceded by two negative excursions of the IMF Bz component with 15-min interval between them, two enhancements of the antisunward convection in the polar cap with the same repetition period, and 15-minute oscillations in geomagnetic H-component in the auroral zone. The distribution of the pulsation intensity along meridian has two local maxima – at equatorial and poleward boundaries of the auroral oval where pulsations occurred in the out-of-phase mode resembling the field-line resonance. At initial stage, the auroral breakup developed as auroral torch stretching and expanding poleward along the meridian. Some later it took a form of the large-scale coiling structure that also distinguishes the considered substorm from classical one. Magnetic, radar and AMPERE satellite data show that before the collapse the coiling structure was located between two field-aligned currents: downward at poleward boundary of structure and upward at equatorial boundary. The set of GEOTAIL satellite and ground data fits to the near-tail current disruption scenario of the substorm onset. We suggest that the 15-min oscillations might play a role in the substorm initiation.

Vladimir V. Safargaleev et al.
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Vladimir V. Safargaleev et al.
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Short summary
Comprehensive analysis of a moderate substorm was performed with using optical observations inside the auroral oval and in the polar cap, combined with data from satellites, radars, and ground magnetometers. The onset took place near the poleward boundary of the auroral oval that is not typical for classical substorms. Data set fits to the near-tail current disruption scenario of the substorm onset. The role of the 15-min oscillations in IMF Bz component in the substorm initiation is discussed.
Comprehensive analysis of a moderate substorm was performed with using optical observations...
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