Abstract
Fluctuation properties of the kinetic Alfven mode such as polarization of the wave electric and magnetic field around the mean magnetic field, parallel fluctuation to the mean field, ratios of the electric to magnetic field, and density fluctuations are analytically estimated by constructing the dielectric tensor of plasma based on the linear Vlasov theory. The dielectric tensor contains various fluid-picture processes in the lowest order, including polarization drift, Hall current, and diamagnetic current. Major discoveries from the dielectric tensor method in the kinetic Alfv\'en mode study are (1) identification of the mechanism of the field rotation sense reversal as a result of competition between the Hall and diamagnetic currents, (2) asymptotic behavior of the parallel magnetic field fluctuation (in the compressive sense). The analytic expression of transport ratios serves as a diagnostic tool to study and identify the kinetic Alfven mode in space plasma observations in the inner heliospheric domain.
Highlights
Kinetic Alfvén mode is one of the small-scale variants of the shear Alfvén mode in which the electric field parallel to the mean magnetic field direction is balanced against the electron-scale Debye screening when the wavevector becomes nearly perpendicular to the mean field [1]
The kinetic Alfvén mode is considered to play an important role in various space plasma environments and is one of the likely fluctuation constituents in solar wind turbulence
Various in situ observations of the solar wind plasma and magnetic field are favorably interpreted as a realization of the kinetic Alfvén mode from 0.1 to 100 Hz in the spacecraft frame (e.g., [2,3,4,5,6,7,8])
Summary
Kinetic Alfvén mode is one of the small-scale variants of the shear Alfvén mode in which the electric field parallel to the mean magnetic field direction (excited nearly in the electromagnetic fashion) is balanced against the electron-scale Debye screening when the wavevector becomes nearly perpendicular to the mean field [1]. The kinetic Alfvén mode is considered to play an important role in various space plasma environments and is one of the likely fluctuation constituents in solar wind turbulence. Various in situ observations of the solar wind plasma and magnetic field are favorably interpreted as a realization of the kinetic Alfvén mode from 0.1 to 100 Hz in the spacecraft frame (e.g., [2,3,4,5,6,7,8]). We revisit the kinetic Alfvén mode and analytically derive the transport ratios and scaling laws for the electric and magnetic fields in the spirit of developing useful tools for the wave mode identification in the spacecraft observations, in view of the inner heliospheric observations, such as Parker Solar Probe, Solar Orbiter, and BepiColombo’s cruise to Mercury. Kinetic Alfvén Mode picture of kinetic Alfvén waves presented in Hollweg [29] by identifying various terms in the dielectric tensor that are physically relevant to the fluid picture, such as the polarization drift, Hall effect, and diamagnetic current
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