Fine structures and dynamics in auroral initial brightening at substorm onsets
We show four auroral initial brightening events at substorm onsets focusing on fine structures and their longitudinal dynamics, which were observed by all-sky TV cameras (30-Hz sampling) on January 2008, in Canada. For two initial brightenings started in the field of views of the cameras, we foun...
| Main Authors: | , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2009-02-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/27/623/2009/angeo-27-623-2009.pdf |
| Summary: | We show four auroral initial brightening events at substorm onsets focusing
on fine structures and their longitudinal dynamics, which were observed by
all-sky TV cameras (30-Hz sampling) on January 2008, in Canada. For two
initial brightenings started in the field of views of the cameras, we found
that they started at longitudinal segments with a size of less than ~30–60 km.
One brightening expanded with wavy structures and the other
expanded as a straight arc. Although the two events had different
structures, both brightening auroras expanded with an average speed of ~20 km/s
in the first 10 s, and ~10 km/s in the following 10 s. The
other two events show that brightening auroras developed with periodic
structures, with longitudinal wavelengths of ~100–200 km. Assuming
that the brightening auroras are mapped to the physical processes occurring
in the plasma sheet, we found that the scale size (30–60 km) and the
expanding speed (20 km/s) of brightening auroras correspond to the order of
ion gyro radii (~500–1400 km) and Alfvén speed or fast ion-flow
speed (~400 km/s), respectively, in the plasma sheet. |
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| ISSN: | 0992-7689 1432-0576 |