A Magnetosphere Wags the Tail Model of Substorms
- Joseph R. Kan,
- Thomas A. Potemra,
- Susumu Kokubun and
- Takesi Iijima
Published Online: 19 MAR 2013
Copyright 1991 by the American Geophysical Union.
How to Cite
Atkinson, G. (1991) A Magnetosphere Wags the Tail Model of Substorms, in Magnetospheric Substorms (eds J. R. Kan, T. A. Potemra, S. Kokubun and T. Iijima), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM064p0191
- Published Online: 19 MAR 2013
- Published Print: 1 JAN 1991
Print ISBN: 9780875900308
Online ISBN: 9781118663981
- Magnetospheric substorms—Congresses
Substorm behaviour in the tail is controlled by processes in the dipole-like region. Consider these processes. There is a steady-state location for the near-earth edge of the plasma sheet which is determined by the physics of Alfvén layers. It is closer to the earth for faster dayside merging rates. In the growth phase, in response to an enhancement of dayside merging, the near-earth plasma sheet moves earthward towards the steady-state location corresponding to the enhanced merging rate. The motion is slow because energy must be extracted from the solar wind. Frequently, the steady-state location is not reached before an expansion is triggered. A subsequent decrease in dayside merging triggers the expansion if the decrease is large enough that the new steady-state location for the near-earth plasma sheet is tailward of its actual location at the time of decrease. Thus a large decrease creates an unstable situation with energetic plasma too close to the earth and too much flux in the tail. The resulting instability can be described as an interchange/ballooning/merging instability with westward drift of energetic particles removing energy from the midnight sector and allowing rapid merging to occur in a localized time slot and causing ballooning to the west. An implication of the model is that merging in the tail is coupled to or controlled by plasma processes on dipole-like flux tubes. There is too much energetic plasma on tail-like flux tubes for them to collapse into a dipole-like configuration. Thus for convection to occur into the dipole-like region, it is necessary that there be an X line near the boundary between tail-like and dipole-like flux tubes. Thus the X line always remains near the boundary and the merging rate must match the earthward convective flow, which is determined by convection processes in the dipolar region.