Properties of short-wavelength oblique Alfvén and slow waves

Journal Article · Wed Oct 01 04:00:00 EDT 2014 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/793/2/107· OSTI ID:22370561

Zhao, J. S.; Wu, D. J. ^[1]; Voitenko, Y. ^[2]; Yu, M. Y. ^[3]

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1. Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)
2. Solar-Terrestrial Centre of Excellence, Space Physics Division, Belgian Institute for Space Aeronomy, Avenue Circulaire 3, B-1180 Brussels (Belgium)
3. Institute for Fusion Theory and Simulation and Department of Physics, Zhejiang University, Hangzhou 310027 (China)

Linear properties of kinetic Alfvén waves (KAWs) and kinetic slow waves (KSWs) are studied in the framework of two-fluid magnetohydrodynamics. We obtain the wave dispersion relations that are valid in a wide range of the wave frequency ω and plasma-to-magnetic pressure ratio β. The KAW frequency can reach and exceed the ion-cyclotron frequency at ion kinetic scales, whereas the KSW frequency remains sub-cyclotron. At β ∼ 1, the plasma and magnetic pressure perturbations of both modes are in anti-phase, so that there is nearly no total pressure perturbations. However, these modes also exhibit several opposite properties. At high β, the electric polarization ratios of KAWs and KSWs are opposite at the ion gyroradius scale, where KAWs are polarized in the sense of electron gyration (right-hand polarized) and KSWs are left-hand polarized. The magnetic helicity σ ∼ 1 for KAWs and σ ∼ –1 for KSWs, and the ion Alfvén ratio R{sub Ai} << 1 for KAWs and R{sub Ai} >> 1 for KSWs. We also found transition wavenumbers where KAWs change their polarization from left-handed to right-handed. These new properties can be used to discriminate KAWs and KSWs when interpreting kinetic-scale electromagnetic fluctuations observed in various solar-terrestrial plasmas. This concerns, in particular, identification of modes responsible for kinetic-scale pressure-balanced fluctuations and turbulence in the solar wind.

• OSTI ID: 22370561
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 793; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ALFVEN WAVES
CYCLOTRON FREQUENCY
CYCLOTRONS
DISPERSION RELATIONS
DISTURBANCES
ELECTRONS
FLUCTUATIONS
HELICITY
MAGNETOHYDRODYNAMICS
PERTURBATION THEORY
PLASMA
POLARIZATION
SOLAR WIND
TURBULENCE
WAVELENGTHS