Energetic ion anisotropies in the geomagnetic tail. 2. Magnetic field and substorm characteristics

Journal Article · Fri Jan 01 04:00:00 EST 1993 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/92JA01657· OSTI ID:6788476

Kettmann, G; Fritz, T A ^[1]; Hones, Jr, E W ^[2]; Daly, P W ^[3]

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1. Los Alamos National Lab, NM (United States)
2. Mission Research Corp., Los Alamos, NM (United States)
3. Max-Planck-Institut fuer Aeronomie, Katlenburg-Lindau (Germany)

We have recently reported results from a survey of strong energetic ion (E > 25 keV) anisotropies in the central geomagnetic tail based on 2 years of data from the ISEE 2 spacecraft. Here we extend this study with particular emphasis on the relation of high ion anisotropies to recent models of geomagnetic substorms and include magnetic field and ground-based data. Beyond 16 R[sub E] downtail distance, we find a correlation between the magnetic field north-south component (B[sub z]) and the streaming direction of the energetic ions. Earthward ion streaming is observed almost exclusively when B[sub z] is positive while tailward streaming tends to occur with negative B[sub z]. Strong ion anisotropies are magnetic field aligned rather than perpendicular to it. A superposed epoch analysis using the AL index yields a relation between substorm phases and the observation of high ion anisotropies. Three events characterized by strong tailward ion and plasma streaming detected first changing to earthward streaming later on are presented in some detail. The overall features of two of these events strongly suggest the formation of a magnetic neutral line earthward of the satellite at substorm onset moving tailward around recovery. While most observations during the third event also indicate such a sequence, there are some puzzling details which do not match this interpretation. We conclude that the statistical properties of strong ion anisotropies can consistently be explained in terms of the near-Earth neutral line model of substorms if the substorm neutral line sometimes forms well inside the ISEE orbit. Other recently published models of substorm onset such as the thermal catastrophe model and the current disruption model can also account for part of the observations but require further refinement. 43 refs., 13 figs.

• OSTI ID: 6788476
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 98:A1; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

661320* -- Auroral
Ionospheric
& Magnetospheric Phenomena-- (1992-)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ANISOTROPY
CHARGED PARTICLES
EARTH ATMOSPHERE
EARTH MAGNETOSPHERE
IONS
MAGNETOTAIL
MATHEMATICAL MODELS
PLASMA
PLASMA SHEET
RADIATION STREAMING
STATISTICAL MODELS