Journal cover Journal topic
Annales Geophysicae An open-access journal of the European Geosciences Union
Ann. Geophys., 27, 623-630, 2009
https://doi.org/10.5194/angeo-27-623-2009
© Author(s) 2009. This work is distributed under
the Creative Commons Attribution 3.0 License.
 
09 Feb 2009

Fine structures and dynamics in auroral initial brightening at substorm onsets
K. Sakaguchi1, K. Shiokawa1, A. Ieda1, R. Nomura1, A. Nakajima1, M. Greffen2, E. Donovan2, I. R. Mann3, H. Kim4, and M. Lessard4 1Solar-Terrestrial Environment Laboratory, Nagoya University, Japan
2Department of Physics and Astronomy, University of Calgary, Alberta, Canada
3Department of Physics, University of Alberta, Alberta, Canada
4Space Science Center, University of New Hampshire, NH, USA
Abstract. 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.

Citation: Sakaguchi, K., Shiokawa, K., Ieda, A., Nomura, R., Nakajima, A., Greffen, M., Donovan, E., Mann, I. R., Kim, H., and Lessard, M.: Fine structures and dynamics in auroral initial brightening at substorm onsets, Ann. Geophys., 27, 623-630, https://doi.org/10.5194/angeo-27-623-2009, 2009.
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