BURST GEOMAGNETIC PULSATIONS AS INDICATORS OF SUBSTORM EXPANSION ONSETS DURING SUPERSTORMS

Le résumé fourni par la source

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 superstorm substorms. For the first time, using the short duration, ∆t < 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

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