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

Abstract

Abstract. 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.

“Obstanovka” experiment on determining spacecraft surface charging aboard the International Space Station

“…In many papers, e.g., [McPherron and Chu, 2018;Stepanov et al, 2021], the mid-latitude positive magnetic bays, associated with "classical" sustorms, are interpreted as the effects of the appearance of the dipolarization process and the substorm West Travelling Surge (WTS) formation. The analysis of the satellites and ground data performed in [Safargaleev et al, 2020] fit to the near-tail current disruption scenario as a possible source of the dipolarization and WTS, associated with polar substorm onset.…”

Fourteenth Workshop Solar Influences on the Magnetosphere, Ionosphere and Atmosphere

“…It is well known that during the low magnetic activity, the night-side magnetosphere substorms and visible auroras are observed at the geomagnetic latitudes higher than the normal auroral oval location so that the auroral oval becomes contracted and poleward shifted. In earlier publications, these high-latitude substorms have been termed as "substorms on contracted oval" [e.g., Akasofu et al, 1973;Lui et al, 1976], later on they were known as "polar substorms" [Kleimenova et al, 2012;Despirak et al, 2014;Safargaleev et al, 2020].…”