Substorm Features in MHD Simulations of Magnetotail Dynamics
- 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
Birn, J. and Hesse, M. (1991) Substorm Features in MHD Simulations of Magnetotail Dynamics, in Magnetospheric Substorms (eds J. R. Kan, T. A. Potemra, S. Kokubun and T. Iijima), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM064p0177
- Published Online: 19 MAR 2013
- Published Print: 1 JAN 1991
Print ISBN: 9780875900308
Online ISBN: 9781118663981
- Magnetospheric substorms—Congresses
We present a review and extended analysis of characteristic results from our three-dimensional resistive MHD simulations of an unstable magnetotail evolution, which develops without the necessity of external driving or prescribed localization of nonideal effects (although in reality these effects may be important). These modes involve magnetic reconnection at a near-Earth site in the tail, consistent with the near-Earth neutral line model of substorms. The evolution tailward of the reconnection site is characterized by plasmoid formation and ejection into the far tail, plasma sheet thinning between the near-Earth neutral line (X line) and the departing plasmoid, and fast tailward flow. This tailward flow, however, occupies large sections of the plasma sheet only at larger distances from the X line, while it occurs spatially and temporally much more limited close to the X line. The region earthward of the X line is characterized by a dipolarization, propagating from midnight toward the flank regions and, perhaps, tailward. It is associated with the signatures of the substorm current wedge: reduction and diversion of part of the cross-tail current from a region surrounding the reconnection site and an increase of region 1 type field-aligned currents. A mapping of these currents to the Earth on the basis of an empirical magnetic field model shows good agreement of the mapped current system with the observed region 1 field-aligned current system and its substorm associated changes, including also a nightward and equatorward shift of the peaks of the field-aligned current density. The evolution of the mappings of the boundaries of the closed field line region bears strong resemblance to the formation and expansion of the auroral bulge. The consistency of all of these details with observed substorm features strongly supports the idea that substorm evolution in the tail is that of a large scale nonideal instability. This does not exclude, however, that external forces are responsible for driving the tail into the unstable regime.