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Quasi-periodic rapid motion of pulsating auroras

机译：Quasi-periodic rapid motion of pulsating auroras

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We report rapid motion of pulsating auroras associated with so called 3 +/- 1 Hz modulations embedded in the main pulsations. During the pulsation ON phase, repetitive expansions are often observed around the edges of pulsating patches. Some events show a few detached expansions traveling away from the main deformed pulsating patch. Approximately 80 of all expansion speeds were found to be less than 70 km s(-1) at ionospheric altitudes, which is less than the projected Alfven speed from the magneto spheric equator to the ionosphere. The rapid motions with speeds of tens of km s(-1) are unlikely to be explained by obliquely propagating chorus elements, which are known to cause the 3 +/- 1 Hz modulation, because the perpendicular speed of the oblique chorus waves is higher than the Alfven speed. We discuss the slow-mode Alfven wave as a candidate modulation source to generate the rapid motions. A few non repetitive expansion events with a speed of more than 150 km s(-1) also appear at the onset of the ON phase. These non-repetitive expanding motions are characterized by a long displacement compared to the repetitive expanding motions. The differences in the expansion speeds indicate different formation mechanisms of the patch motions. (C) 2016 Elsevier B.V. and NIPR. All rights reserved.

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