Compressibility and cyclotron damping in the oblique Alfven wave

Journal Article · Wed Nov 01 04:00:00 EST 1989 · Journal of Geophysical Research; (USA)

DOI:https://doi.org/10.1029/JA094iA11p15399· OSTI ID:5834827

Harmon, J K ^[1]

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1. National Astronomy and Ionosphere Center, Arecibo (Puerto Rico)

Compressibility, magnetic compressibility, and damping rate are calculated for the obliquely propagating Alfven shear wave in high- and low-beta Vlasov plasmas. There is an overall increase in compressibility as beta is reduced from {beta} = 1 to {beta}{much lt}1. For high obliquity {theta} and low frequency ({omega} {much lt} {Omega}{sub p}) the compressibility C follows a k{sup 2} wave number dependence; for high {theta} and low {beta} the approximation C(k) {approx} k{sub n}{sup 2} {identical to} (kV{sub A}/{Omega}{sub p}){sup 2} holds for wave numbers up to the proton cyclotron resonance, where {Omega}{sub p} is the proton cyclotron frequency and V{sub A} is the Alfven velocity. Strong proton cyclotron damping sets in at k{sub n} of the order of unity; the precise k{sub n} position of the damping cutoff increases with decreasing {beta} and increasing {theta}. Hence compressibility can exceed unity near the damping cutoff for high-{theta} waves in a low-{beta} plasma. The magnetic compressibility of the oblique Alfven wave also has a k{sup 2} dependence and can reach a maximum value of the order of 10% at high wave number. It is shown that Alfven compressibility could be the dominant contributor to the near-Sun solar wind density fluctuation spectrum for k>10{sup {minus}2} km{sup {minus}1} and hence might cause some of the flattening at high wave number seen in radio scintillation measurements. This would also be consistent with the notion that the observed density spectrum inner scale is a signature of cyclotron damping.

• OSTI ID: 5834827
• Journal Information: Journal of Geophysical Research; (USA), Journal Name: Journal of Geophysical Research; (USA) Vol. 94:A11; ISSN 0148-0227; ISSN JGREA
• Country of Publication: United States
• Language: English

Related Subjects

640104* -- Astrophysics & Cosmology-- Solar Phenomena
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
ALFVEN WAVES
BETA RATIO
COMPRESSIBILITY
DAMPING
DISTANCE
ENERGY LOSSES
HYDROMAGNETIC WAVES
LOSSES
MAIN SEQUENCE STARS
MECHANICAL PROPERTIES
PLASMA
SCINTILLATIONS
SHEAR
SOLAR ACTIVITY
SOLAR WIND
STARS
SUN
WAVE PROPAGATION