Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
5780576 | Polar Science | 2016 | 9 Pages |
Abstract
We report rapid motion of pulsating auroras associated with so called â3 ± 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 sâ1 at ionospheric altitudes, which is less than the projected Alfvén speed from the magnetospheric equator to the ionosphere. The rapid motions with speeds of tens of km sâ1 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 Alfvén speed. We discuss the slow-mode Alfvén 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 sâ1 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.
Related Topics
Physical Sciences and Engineering
Earth and Planetary Sciences
Earth and Planetary Sciences (General)
Authors
Yoko Fukuda, Ryuho Kataoka, Yoshizumi Miyoshi, Yuto Katoh, Takanori Nishiyama, Kazuo Shiokawa, Yusuke Ebihara, Donald Hampton, Naomoto Iwagami,