Polar substorm on 7 December 2015: preonset phenomena and features of auroral breakup
<p>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 au...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-07-01
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| Series: | Annales Geophysicae |
| Online Access: | https://angeo.copernicus.org/articles/38/901/2020/angeo-38-901-2020.pdf |
| Summary: | <p>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) <span class="inline-formula"><i>B</i><i>z</i></span> 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 <span class="inline-formula"><i>H</i></span> 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.</p> |
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| ISSN: | 0992-7689 1432-0576 |