Source of the backstreaming ion beams in the foreshock region

Journal Article · Fri Apr 01 04:00:00 EST 1983 · J. Geophys. Res.; (United States)

DOI:https://doi.org/10.1029/JA088iA04p03046· OSTI ID:6084108

Tanaka, M; Goodrich, C C; Winske, D; Papadopoulos, K

A new source mechanism is proposed for the 'reflected' ion beams observed in the foreshock region of the earth's bow shock. In our model the beams originate in the magnetosheath downstream of the qausi-perpendicular portion of the shock. The quasi-perpendicular shock transition is characterized by two downstream ion populations including high-energy gyrating ions in addition to the directly transmitted anisotropic ions. We show by particle simulations that this highly anisotropic downstream ion distribution (T/sub perpendicular//T/sub parallel/ >>1) can excite electromagnetic ion cyclotron waves which, in turn, pitch angle scatter the gyrating ions in a few ion gyroperiods. As a result, some ions acquire large parallel velocities and move fast enough along the convecting downstream magnetic field to escape back across the bow shock into the upstream region. The distribution of escaping ions calculated by using the pitch-angle-scattered ions, as a source, becomes a beam with a large temperature anisotropy T/sub perpendicular/ approx.3--5 T/sub parallel/ and a mean velocity along the magnetic field of about twice that of the solar wind velocity. A significant result is the presence of the maximum angle theta/sub n/B = theta/sub c/ above which no ions can escape, where theta/sub n/B is the angle between the shock normal and the interplanetary magnetic field. A wide peak of constant escaping ion flux is formed below theta/sub c/ whose number density is 1--2% of that of the solar wind. These results are in general agreement with the ISEE observations of the 'reflected' ions.

• Research Organization: Institute for Physical Science and Technology, University of Maryland, College Park, Maryland 20742
• OSTI ID: 6084108
• Journal Information: J. Geophys. Res.; (United States), Journal Name: J. Geophys. Res.; (United States) Vol. 88:A4; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

640203* -- Atmospheric Physics-- Magnetospheric Phenomena-- (-1987)
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BEAMS
EARTH ATMOSPHERE
ION BEAMS
MAGNETOSHEATH
MAGNETOSPHERE
REFLECTION
SHOCK WAVES