Radial expansion of the tail current disruption during substorms: A new approach to the substorm onset region

Journal Article · Sun Mar 01 04:00:00 EST 1992 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/91JA02470· OSTI ID:5398199

Ohtani, S ^[1]; Kokubun, S ^[2]; Russell, C T ^[3]

---

1. John Hopkins Univ., Laurel, MD (United States)
2. Univ. of Tokyo (Japan)
3. Univ. of California, Los Angeles (United States)

The substorm onset region and the radial development of the tail current disruption are examined from a new viewpoint. The reconfiguration of the magnetotail field at substorm onset can be understood in terms of a sudden decrease (disruption) in tail current intensity. The north-south component (B{sub Z}) is very sensitive to whether the spacecraft position is earthward or tailward of the disruption region, while the change in Sun-Earth component (B{sub X}) is most sensitive to the change in tail current intensity near the spacecraft. If the current disruption starts in a localized range of radial distance and expands radially, a distinctive phase relationship between the changes in B{sub X} and B{sub Z} is expected to be observed. This phase relationship depends on whether the current disruption starts on the earthward side or the tailward side of the spacecraft. Thus it is possible to infer the direction of the radial expansion of the current disruption from magnetic field data of a single spacecraft. This method is applied to ISEE observations of a tail reconfiguration event that occurred on March 6, 1979. The phase relationship indicates that eh disruption region expanded tailward from the earthward side of the spacecraft during the event. This model prediction is consistent with the time lag of magnetic signatures observed by the two ISEE spacecraft. The expansion velocity is estimated at 2 R{sub E}/min ({approximately}200 km/s) for this event. Furthermore, it is found that the observed magnetic signatures can be reproduced to a good approximation by a simple geometrical model of the current disruption. The method is used statistically for 13 events selected from the ISEE magnetometer data. It is found that the current disruption usually starts in the near-Earth magnetotail ({vert bar}X{vert bar} < 20 R{sub E}) and often within 15 R{sub E} of the Earth.

• OSTI ID: 5398199
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 97:A3; ISSN 0148-0227; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

661320* -- Auroral
Ionospheric
&amp; Magnetospheric Phenomena-- (1992-)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COMPARATIVE EVALUATIONS
CURRENTS
EARTH ATMOSPHERE
EARTH MAGNETOSPHERE
ELECTRIC CURRENTS
EVALUATION
EXPANSION
MAGNETIC BAYS
MAGNETIC FIELD CONFIGURATIONS
MAGNETOTAIL
MATHEMATICAL MODELS
MATHEMATICS
PLASMA SHEET
STATISTICS