| GEOPHYSICS, ASTRONOMY, AND ASTROPHYSICS |
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The Wave-Like Auroral Structure around Auroral Expansion Onset |
| TANG Chao-Ling**
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School of Space Science and Physics, Shandong University at Weihai, Weihai 264209
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| Cite this article: |
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TANG Chao-Ling 2011 Chin. Phys. Lett. 28 109401 |
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Abstract We present the direct connection between the wave-like auroral structure around the time of auroral expansion onset and the ballooning mode waves in the near-Earth magnetotail. Based on the NASA mission time history of events and macroscale interactions during substorms (THEMIS) ground-based all-sky imagers, we show that around the time of auroral expansion onset, a wave-like auroral structure first has four luminosity peaks separated by 2–3° magnetic longitude (MLON). Subsequently, the wave-like structure propagates in the azimuthal direction and an overall bright arc spans approximately 1 h magnetic local time. The wavelength is estimated to be 120–180 km. Finally, a noticeable poleward auroral expansion is observed. The ballooning mode waves are identified by two THEMIS probes in the near-Earth magnetotail. The observed wavelength of the ballooning mode waves is approximately equal to the order of the ion Larmor radius. The wavelength of 1500–3000 km in the near-Earth magnetotail is comparable with the wave-like auroral structure estimate. This study suggests that the ballooning mode waves might play a crucial role in auroral expansion onset, corresponding to the wave-like auroral structure in this study.
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| Keywords:
94.30.cq
94.30.Lr
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Received: 12 April 2011
Published: 28 September 2011
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| PACS: |
94.30.cq
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(MHD waves, plasma waves, and instabilities)
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94.30.Lr
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(Magnetic storms, substorms)
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