Ion anisotropy instabilities in the magnetosheath

Journal Article · Mon Feb 01 00:00:00 EST 1993 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/92JA01844· OSTI ID:7061167

Gary, S P ^[1]; Fuselier, S A ^[2]; Anderson, B J ^[3]

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1. Los Alamos National Lab., NM (United States)
2. Lockheed Palo Alto Research Lab., CA (United States)
3. Johns Hopkins Univ., Laurel, MD (United States)

Recent observations in Earth's magnetosheath have delineated several different kinds of magnetic fluctuation spectra below the proton cyclotron frequency. This paper provides a theoretical interpretation for some of these observations, describing solutions of the linear Vlasov dispersion equation for fully electromagnetic instabilities for particle distributions which model those observed in the magnetosheath. The model assumes a high-[beta], homogeneous plasma with bi-Maxwellian, anisotropic (T[sub [perpendicular]p]/T[sub [parallel]p]) protons; a similarly anisotropic, tenuous, doubly ionized helium component; and isotropic cool electrons. This model also assumes a uniform magnetic field and no relative average drifts among the components. This model yields three growing modes: the proton cyclotron anisotropy, the helium cyclotron anisotropy, and the mirror instabilities. The regimes in [beta][sub p] versus T[sub [perpendicular]p]/T[sub [parallel]p] space which correspond to maximum growth rates of the mirror and proton cyclotron anisotropy instabilities are computed, including helium densities appropriate for the magnetosheath; the results show very good agreement with the observations of mirror-like and proton-cyclotron-like events. This agreement with observations implies that the transition between cyclotron and mirror fluctuation dominance is consistent with linear theory. 33 refs., 7 figs., 1 tab.

• OSTI ID: 7061167
• Journal Information: Journal of Geophysical Research; (United States), Vol. 98:A2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
MAGNETOSHEATH
MATHEMATICAL MODELS
PLASMA INSTABILITY
COMPARATIVE EVALUATIONS
ANISOTROPY
CYCLOTRON FREQUENCY
ELECTRONS
FLUCTUATIONS
HELIUM IONS
HOMOGENEOUS PLASMA
INSTABILITY GROWTH RATES
MAGNETIC FIELDS
SPACE
CHARGED PARTICLES
ELEMENTARY PARTICLES
EVALUATION
FERMIONS
INSTABILITY
IONS
LEPTONS
PLASMA
VARIATIONS
661320* - Auroral
Ionospheric
& Magnetospheric Phenomena- (1992-)