The proton cyclotron instability and the anisotropy/{beta} inverse correlation

Journal Article · Fri Apr 01 04:00:00 EST 1994 · Journal of Geophysical Research

DOI:https://doi.org/10.1029/93JA03583· OSTI ID:121231

Gary, S P; McKean, M E; Winske, D ^[1]; Anderson, B J ^[2]; Denton, R E ^[3]; Fuselier, S A ^[4]

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

Spacecraft observations in the strongly compressed subsolar magnetosheath show an inverse correlation between the proton temperature anisotropy (T{sub {perpendicular}p}/T{sub {parallel}p} > 1 where {perpendicular} and {parallel} denote directions perpendicular and parallel to the background magnetic field) and the parallel proton {beta}({beta}{sub {parallel}p}). This manuscript uses one-dimensional hybrid simulations of the proton cyclotron anisotropy instability in homogeneous electron-proton plasmas to study this correlation which may represent a limited closure relation for fluid theories of anisotropic space plasmas. The emphasis is on driven simulations which increase the temperature anisotropy by periodically reducing the magnetic-field-aligned velocities of the protons. The late-time states from ensembles of both initial value and driven simulations yield very similar expressions for the proton anisotropy/{beta}{sub {parallel}p} inverse correlation, and provide a basis for explaining differences between sheath observations from different spacecraft. The driven simulations also yield expressions for the maximum instability growth rate and the fluctuating field energy as functions of {beta}{sub {parallel}p} and a parameter characterizing the anisotropy driver. 50 refs., 5 figs.

• OSTI ID: 121231
• Journal Information: Journal of Geophysical Research, Journal Name: Journal of Geophysical Research Journal Issue: A4 Vol. 99; ISSN JGREA2; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
ANISOTROPY
BETA RATIO
CYCLOTRON INSTABILITY
MAGNETOSHEATH
PROTON TEMPERATURE