Particle and Field Signatures of Substorms in the Near Magnetotail
- Edward W. Hones Jr.
Published Online: 19 MAR 2013
Copyright 1984 by the American Geophysical Union.
Magnetic Reconnection in Space and Laboratory Plasmas
How to Cite
Baker, D. N. (1984) Particle and Field Signatures of Substorms in the Near Magnetotail, in Magnetic Reconnection in Space and Laboratory Plasmas (ed E. W. Hones), American Geophysical Union, Washington, D. C.. doi: 10.1029/GM030p0193
- Published Online: 19 MAR 2013
- Published Print: 1 JAN 1984
Print ISBN: 9780875900582
Online ISBN: 9781118664223
- Interplanetary magnetic field (IMF);
- Magnetic merging;
- Magnetospheric system;
- Substorm expansion onset
The near-earth magnetotail (10 ≤ r ≤ 20 RE) portion of the terrestrial magnetosphere is very likely the region in which magnetospheric substorms are initiated. An observational advantage compared to other astrophysical regions is that the near magnetotail can be nearly continuously monitored by spacecraft that are relatively fixed in location. Based on numerous case studies, it is found thai southward IMF is clearly related to increased energy input to the magnetosphere which manifests itself as an increase of magnetotail currents and field strength, while northward IMF “turns off” energy input and rapidly stops the progress of energy storage in the tail field. In studying hundreds of substorm events near local midnight with geostationary spacecraft instrumentation, we have found that most substorm injection events are preceded by cigar (growth) phase features (i.e., j‖ > j⟂ for energetic electron distributions). In one particular study, for more than 100 cases of detected cigar phases, in 97 cases the cigar phase was terminated by a substorm injection event. In only 4 cases did a cigar occur with no identifiable substorm onset. Such results suggest that substorm expansion onsets occur if, and only if, stored magnetotail energy is increased above a quiet time level. We conclude that observations in the near-earth magnetotail show some of the clearest and most repeatable signatures available in support of the concept of loading and unloading of magnetic energy in association with substorms. The data illustrate that magnetic energy is accumulated and stored for 0.5∼2.0 hours in the tail lobes and then is rapidly dissipated at substorm expansion on set. The dissipation is manifested by the acceleration and rapid transport of hot plasma and energetic particle populations within the near-tail region. These energized plasmas provide an excellent tracer capability which allows a relatively clear determination of where, when, and how magnetic energy is converted to other forms during substorms. When near-tail data are considered in a global context of deep-tail measurements, numerical models, ground-based data, etc., they provide very strong evidence for the neutral line substorm model and, thus, for the regular occurrence of magnetic reconnection in the near-earth magnetotail.