We report on the dynamics of field‐aligned currents (FACs), broadband geomagnetic pulsations, and airglow obtained from the Irkutsk (IRK), Mondy (MND), and Borok (BOX) midlatitude geomagnetic observatories and the Tory (TOR) optical observatory during storm substorms. For the first time, using the short duration, Δt < 0.5 min, high‐frequency component of the burst pulsations (Pi1B), we determined the substorm double expansion phase (EP) onsets <5 min apart, which is hardly possible by means of the low‐frequency (periods of 2–5 min) Psc/PiB pulsations. We argue that the observed burst pulsations are the result of prompt changes in the solar wind dynamic pressure and/or the current circuit related to the westward electrojet. Each pulsed source can excite short bursts of broadband electromagnetic modes of the ionospheric Alfvén resonator in the range of short‐period pulsations with a periodic resonance structure of the spectrum characteristic of the observed Pi1B/Psc pulsations.

中文翻译：

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爆发期间地磁脉动是暴风雨中亚暴扩张开始的指标

我们报告了在伊尔库茨克（IRK），蒙迪（MND）和Borok（BOX）中纬度地磁观测站和托里（TOR）光学观测站获得的场对准电流（FAC），宽带地磁脉动和气辉的动力学风暴。首次使用短时间Δt <0.5分钟，爆发脉动（Pi1B）的高频分量，我们确定了亚暴双膨胀相（EP）的发作间隔<5分钟，这几乎不可能通过低频（2-5分钟）来实现）Psc / PiB脉动。我们认为，观测到的突发脉动是太阳风动压力和/或与西电喷射有关的电流回路迅速变化的结果。每个脉冲源都可以在短周期脉动范围内激发电离层Alfvén谐振器的宽带电磁模式的短脉冲，并具有观察到的Pi1B / Psc脉动的频谱特征的周期性谐振结构。