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.

中文翻译：

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2015 年 12 月 7 日的极地亚暴：极光分裂的先兆现象和特征

摘要。使用在极光椭圆内和极冠中的同步光学观测，结合来自卫星、雷达和地面磁力计的数据，对中等强度 600 nT 亚暴进行了综合分析。爆发发生在极光椭圆的极地边界附近，这对于经典亚暴来说并不典型。亚暴爆发之前有两次行星际磁场 (IMF) Bz 分量的负偏移，它们之间的间隔为 1 分钟，极冠中反太阳对流的两次增强以相同的时间间隔，以及 15 分钟的振荡。极光带中的地磁 H 分量。脉动强度沿子午线的分布有两个局部最大值，即在极光椭圆的赤道和极地边界处，其中脉动发生在类似于场线共振的异相模式中。在初始阶段，随着极光火炬沿子午线向极地伸展和扩展，极光分裂发展。后来它采用了大规模盘绕结构的形式，这也将所考虑的亚暴与经典亚暴区分开来。磁、雷达和有源磁层和行星电动力学响应实验（AMPERE）卫星数据表明，在坍塌之前，盘绕结构位于两个磁场对齐的电流之间，即在结构的极地边界向下和在赤道向上边界。GEOTAIL 卫星和地面数据集适合亚暴爆发的近尾电流中断情景。