Periodic Restructuring of Auroral Arcs as an Indicator of Alfvén Resonance in the Region of Substorm Onset

Autor: T. A. Kornilova, I. V. Golovchanskaya
Rok vydání: 2018
Předmět:
Zdroj: Geomagnetism and Aeronomy. 58:307-313
ISSN: 1555-645X
0016-7932
DOI: 10.1134/s001679321803009x
Popis: Using optical data from observatories of the Polar Geophysical Institutes, as well all-sky TV observations at Canadian stations of ground support for the THEMIS satellite mission, we clarify whether Alfven resonance should necessarily be present in the region of subsequent substorm onset. If this is true, the diversion of magnetospheric cross-tail current to the ionosphere, which leads to substorm onset, may be due to resonant Alfven (or flapping) oscillations that increase in duration. This possibility is believed to indicate optically the presence of Alfven resonance via periodic restructuring of the preonset auroral arc 3–15 min before onset at T 0 . At the latitudes of the observatories included in this study, auroral restructuring occurs as repetitive poleward excursions of the preonset arc (the periods of excursions are 1–3 min) and can be readily explained by the theory of Alfven resonance. It is shown that this feature, while typically observed in strong substorm events, may be lacking for weaker substorms. As proved by conjugate satellite observations, the lack of auroral restructuring in the latter case may result from the weakness of the involved Alfven resonance, which is still present but not accompanied by large field-aligned currents sufficient for visualization in the ionosphere of the apparent propagation of oscillation phase across the resonance layer.
Databáze: OpenAIRE
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