University of Oulu

Safargaleev, V. V., Kozlovsky, A. E., and Mitrofanov, V. M.: Polar substorm on 7 December 2015: preonset phenomena and features of auroral breakup, Ann. Geophys., 38, 901–918,, 2020

Polar substorm on 7 December 2015 : preonset phenomena and features of auroral breakup

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Author: Safargaleev, Vladimir V.1; Kozlovsky, Alexander E.2; Mitrofanov, Valery M.1
Organizations: 1Polar Geophysical Institute, Apatity, Russia
2Sodankylä Geophysical Observatory, Sodankylä, Finland
Format: article
Version: published version
Access: open
Online Access: PDF Full Text (PDF, 7.9 MB)
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Language: English
Published: Copernicus Publications, 2020
Publish Date: 2020-09-07


Comprehensive analysis of a moderate 600 nT substorm was performed 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 interplanetary magnetic field (IMF) Bz component, with a 1 min interval between them, two enhancements of the antisunward convection in the polar cap with the same time interval, and 15 min oscillations in the geomagnetic H component in the auroral zone. The distribution of the pulsation intensity along meridian has two local maxima, namely at the equatorial and poleward boundaries of the auroral oval, where pulsations occurred in the out-of-phase mode resembling the field line resonance. At the initial stage, the auroral breakup developed as the auroral torch stretched and expanded poleward along the meridian. Later it took the form of the large-scale coiling structure that also distinguishes the considered substorm from the classical one. Magnetic, radar, and the Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE) satellite data show that, before the collapse, the coiling structure was located between two field-aligned currents, namely downward at the poleward boundary of structure and upward at the equatorial boundary. The set of GEOTAIL satellites and ground data fit 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.

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Series: Annales geophysicae
ISSN: 0992-7689
ISSN-E: 1432-0576
ISSN-L: 0992-7689
Volume: 38
Issue: 4
Pages: 901 - 918
DOI: 10.5194/angeo-38-901-2020
Type of Publication: A1 Journal article – refereed
Field of Science: 115 Astronomy and space science
Funding: The research of Vladimir V. Safargaleev was supported by the Academy of Finland (grant no. 316991).
Copyright information: © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License.