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Author Verscharen, Daniel ♦ Chen, Christopher H. K. ♦ Wicks, Robert T.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword ASTROPHYSICS, COSMOLOGY AND ASTRONOMY ♦ AMPLITUDES ♦ ANISOTROPY ♦ COMPARATIVE EVALUATIONS ♦ DISPERSION RELATIONS ♦ DISPERSIONS ♦ FLUCTUATIONS ♦ FORECASTING ♦ HIGH-BETA PLASMA ♦ LANDAU LIQUID HELIUM THEORY ♦ MAGNETOHYDRODYNAMICS ♦ POLARIZATION ♦ SIMULATION ♦ SOLAR WIND ♦ TURBULENCE ♦ VELOCITY
Abstract Observations in the solar wind suggest that the compressive component of inertial-range solar-wind turbulence is dominated by slow modes. The low collisionality of the solar wind allows for nonthermal features to survive, which suggests the requirement of a kinetic plasma description. The least-damped kinetic slow mode is associated with the ion-acoustic (IA) wave and a nonpropagating (NP) mode. We derive analytical expressions for the IA-wave dispersion relation in an anisotropic plasma in the framework of gyrokinetics and then compare them to fully kinetic numerical calculations, results from two-fluid theory, and magnetohydrodynamics (MHD). This comparison shows major discrepancies in the predicted wave phase speeds from MHD and kinetic theory at moderate to high β . MHD and kinetic theory also dictate that all plasma normal modes exhibit a unique signature in terms of their polarization. We quantify the relative amplitude of fluctuations in the three lowest particle velocity moments associated with IA and NP modes in the gyrokinetic limit and compare these predictions with MHD results and in situ observations of the solar-wind turbulence. The agreement between the observations of the wave polarization and our MHD predictions is better than the kinetic predictions, which suggests that the plasma behaves more like a fluid in the solar wind than expected.
ISSN 0004637X
Educational Use Research
Learning Resource Type Article
Publisher Date 2017-05-10
Publisher Place United States
Journal Astrophysical Journal
Volume Number 840
Issue Number 2


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