Development of substorms in the near-Earth tail Original Research Article

For substorm onsets, earthward flowing ions appear as an initial signal of the onset in the near-Earth plasma sheet in the onset sector. The flow activity in the onset sector is followed by a step-like increase in the Bz field in the equatorial plane, which results in a dipolarization in the field. The field change is usually associated with energization in ions and electrons. Outside of the onset sector the field dipolarization takes place. However, it may not be preceded by earthward flowing ions, and ions usually have the duskward flows in the evening sector and the dawnward flows in the morning sector. The onset signatures at synchronous orbit are delayed relative to those beyond 10 RE.