Mirror and ion cyclotron anisotropy instabilities in the magnetosheath

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

DOI:https://doi.org/10.1029/92JA01842· OSTI ID:6902422

McKean, M E; Winske, D; Gary, S P ^[1]

---

1. Los Alamos National Lab., NM (United States)

Magnetosheath plasmas are typically characterized by a proton [beta] > 1 and a proton temperature anisotropy T[sub [perpendicular]]/T[sub [parallel]] > 1. Such a plasma is unstable to both the ion cyclotron anisotropy and mirror instabilities, and evidence for both of these growing modes has been found in the magnetosheath. In this paper, the authors use one-dimensional hybrid simulations to investigate the kinetic properties of these two instabilities. They find that, for moderate values of ion [beta] and temperature anisotropy, the two instabilities produce similar levels of turbulence, but that the cyclotron instability apparently produces higher fluctuation levels than the mirror instability for high [beta] or anisotropy. Although both instabilities saturate by reducing the ion temperature anisotropy, mirror waves accomplish this through the use of the wave magnetic fields, whereas cyclotron waves do so by using the wave electric fields in resonant interactions with the ions. Consequently, mirror waves preferentially affect those ions with large magnetic moment, while cyclotron waves affect a broader range of ions and thereby dominate the isotropization process even when the mirror mode is somewhat stronger. They also investigate the utility of transport ratios as mode identifiers, and find that the Alfven ratio in particular can be useful in distinguishing between the two modes.

• OSTI ID: 6902422
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 97:A12; 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
ELECTRIC FIELDS
FLUCTUATIONS
INSTABILITY
KINETICS
MAGNETIC FIELDS
MAGNETOSHEATH
PLASMA INSTABILITY
PLASMA WAVES
PROTON TEMPERATURE
TURBULENCE
VARIATIONS