Particle signatures of magnetic topology at the magnetopause: AMPTE/CCE observations

Journal Article · Sat Jul 01 04:00:00 EDT 1995 · Journal of Geophysical Research

DOI:https://doi.org/10.1029/94JA02811· OSTI ID:223558

Fuselier, S A ^[1]; Anderson, B J ^[2]; Onsager, T G ^[3]

---

1. Lockheed Palo Alto Lab., CA (United States)
2. Johns Hopkins Univ., Laurel, MD (United States)
3. Univ. of New Hampshire, Durham, NH (United States)

Electron distributions at energies above 50 eV have been found to be a sensitive indicator of magnetic topology for magnetopause crossings of the AMPTE/CCE spacecraft. Progressing from the magnetosheath to the magnetosphere two abrupt transitions occur. First, the magnetosheath electron population directed either parallel or antiparallel to the magnetic field is replaced by a streaming, heated magnetosheath electron population. The other half of the distribution is unchanged. The region with unidirectional, heated magnetosheath electrons is identified as the magnetosheath boundary layer (MSBL). Second, the unheated magnetosheath electron population is replaced by a heated population nearly identical to the population encountered in the MSBL, resulting in a symmetric counterstreaming distribution. The region populated by the bidirectional heated magnetosheath electrons is identified as the low-latitude boundary layer (LLBL). The MSBL and LLBL identified by the electron transitions are the same as the regions identified using ion composition measurements. The magnetosheath-MSBL transition reflects a change in magnetic topology from a solar wind field line to one that threads the magnetopause, and the existence of a magnetosheath-MSBL transition implies that the magnetopause is open. When the current layer is easily identified, the MSBL-LLBL transition coincides with the magnetopause current layer, indicating that the magnetosheath electrons are heated in the current layer. Both magnetosheath-MSBL and MSBL-LLBL transitions are observed for low as well as high magnetic shears. Moreover, the transitions are particularly clear for low shear implying that magnetic topology boundaries are sharp even when abrupt changes in the field and other plasma parameters are absent. These observations are consistent with quasi-steady, high-latitude reconnection and indicate that the signatures of this reconnection geometry are commonly present in the subsolar region. 32 refs., 10 figs.

• OSTI ID: 223558
• Journal Information: Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: A7 Vol. 100; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
BOUNDARY LAYERS
DISTRIBUTION FUNCTIONS
ELECTRONS
MAGNETIC RECONNECTION
MAGNETOPAUSE