Low-Frequency Waves in the Near-Earth Magnetotail before Substorm Expansion Onsets
Abstract
Magnetic reconnection and dipolarization, which occur in the near-Earth magnetotail just before substorm expansion onsets, are important processes for the substorm triggering. To understand the triggering of these processes, we have investigated low-frequency waves that were observed in the near-Earth magnetotail before onsets, by performing statistical analysis based on Geotail observations and case studies based on multi-point THEMIS and Geotail observations. Here we focused our examination on ~10 min interval before onsets. We find that small-amplitude Alfven and slow-mode magnetosonic waves with a period of ~1 to 2 min continuously exist for more than 10 min before onsets. Such waves are seen not only in the initial dipolarization region but also midway between the magnetic reconnection and initial dipolarization regions. It seems that the amplitudes of the waves are larger in the off-equator plasma sheet and the plasma sheet boundary layer than at the magnetic equator and in the lobe. After onsets the waves considerably amplify in the plasma sheet. These results may imply that instabilities already begin to grow gradually in a wide region during the substorm growth phase, while their explosive growth begins in localized regions just before onsets.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMSM11B2088M
- Keywords:
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- 2790 MAGNETOSPHERIC PHYSICS Substorms;
- 2744 MAGNETOSPHERIC PHYSICS Magnetotail;
- 2752 MAGNETOSPHERIC PHYSICS MHD waves and instabilities;
- 2740 MAGNETOSPHERIC PHYSICS Magnetospheric configuration and dynamics