The effect of oxygen ions on the stability and polarization of Kinetic Alfvén Waves in the magnetosphere (original) (raw)
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Alfvén waves in the magnetosphere generated by shock wave / plasmapause interaction
Solnechno-Zemnaya Fizika, 2019
We study Alfvén waves generated in the magnetosphere during the passage of an interplanetary shock wave. After shock wave passage, the oscillations with typical Alfvén wave dispersion have been detected in spacecraft observations inside the magnetosphere. The most frequently observed oscillations are those with toroidal polarization; their spatial structure is described well by the field line resonance (FLR) theory. The oscillations with poloidal polarization are observed after shock wave passage as well. They cannot be generated by FLR and cannot result from instability of high-energy particle fluxes because no such fluxes were detected at that time. We discuss an alternative hypothesis suggesting that resonant Alfvén waves are excited by a secondary source: a highly localized pulse of fast magnetosonic waves, which is generated in the shock wave/plasmapause contact region. The spectrum of such a source contains oscillation harmonics capable of exciting both the toroidal and poloid...
Monthly Notices of the Royal Astronomical Society, 2019
Thanks to the evidence provided by the Cassini spacecraft mission, it is now established that Saturn's magnetospheric plasma consists of various types of positive ions, as well as two distinct populations of electrons, at different temperatures. The electron population energy distributions are characterized by long suprathermal tails and have been effectively modelled by kappa-type distributions. Plasma properties are known to vary along the radial direction. A strong magnetic field penetrates the magnetosphere, hence the plasma beta is small, β < 1 for radial distance < 15.2 R S (where R S = 60 330 km is the Saturn's radius). Motivated by these observations, we have investigated the conditions for existence and the dynamics of linear and non-linear kinetic Alfvén waves (KAWs) in Saturn's magnetosphere. We have considered a low-β (strongly magnetized) plasma, comprising of positive ions and two electron populations ('cold' and 'hot') characterized by non-Maxwellian (kappa) distributions. In the small-amplitude regime, harmonic analysis leads to a linear dispersion relation bearing explicit dependence on the characteristics of the suprathermal components. In the nonlinear regime, large-amplitude stationary profile kinetic Alfvén solitary wave solutions are obtained via a two-component pseudopotential method, associated with either positive or negative potential structures (pulses) propagating at sub-and super-Alfvénic speeds, respectively. The effect of various intrinsic plasma configuration properties (hot-to-cold electron density and temperature ratio; superthermality indices κ c and κ h ; plasma beta) as well as propagation parameters (pulse speed, direction of propagation) on the characteristics of KAW solitary waves are discussed.
High-frequency Alfvén waves in multi-ion coronal plasma: Observational implications
Journal of Geophysical Research: Space Physics, 2005
We investigate the effects of high-frequency (of order ion gyrofrequency) Alfvén and ion-cyclotron waves on ion emission lines by studying the dispersion of these waves in a multi-ion coronal plasma. For this purpose we solve the dispersion relation of the linearized multifluid and Vlasov equations in a magnetized multi-ion plasma with coronal abundances of heavy ions. We also calculate the dispersion relation using nonlinear one-dimensional hybrid kinetic simulations of the multi-ion plasma. When heavy ions are present the dispersion relation of parallel propagating Alfvén cyclotron waves exhibits the following branches (in the positive W À k quadrant): right-hand polarized nonresonant and left-hand polarized resonant branch for protons and each ion. We calculate the ratio of ion to proton velocities perpendicular to the direction of the magnetic field for each wave modes for typical coronal parameters and find strong enhancement of the heavy ion perpendicular fluid velocity compared with proton perpendicular fluid velocity. The linear multifluid cold plasma results agree with linear warm plasma Vlasov results and with the nonlinear hybrid simulation model results. In view of our findings we discuss how the observed nonthermal line broadening of minor ions in coronal holes may relate to the high-frequency wave motions.
Kinetic Alfvén waves and plasma transport at the magnetopause
Geophysical Research Letters, 1997
Large amplitude compressional type ULF waves can propagate from the magnetosheath to the magnetopause where there are large gradients in density, pressure and magnetic field. These gradients efficiently couple compressional waves with shear/kinetic Alfv6n waves near the Alfv6n fieldline resonance location (w -kllVA). We present a solution of the kinetic-MHD wave equations for this process using a realistic equilibrium profile including full ion Larmor radius effects and wave-particle resonance interactions for electrons and ions to model the dissipation. For northward IMF a KAW propagates backward to the magnetosheath. For southward IMF the wave remains in the magnetopause but can propagate through the kll -0 location. The quasilinear theory predicts that transport due to KAWs at the magnetopause primarily results from the perpendicular electric field coupling with magnetic drift effects with diffusion coefficient Dñ ,-• 109 m2/s. For southward IMF additional transport can occur because magnetic islands form at the /Oil -0 location. Due to the broadband nature of the observed waves these islands can overlap leading to stochastic transport which is larger than that due to quasilinear effects.
Journal of Geophysical Research: Space Physics, 2015
The mutual nonlinear interplay of kinetic Alfvén wave (KAW) and ion acoustic wave, for the high-β plasma (i.e., m e /m i ≪ β ≪ 1, where β is thermal to magnetic pressure ratio) in the magnetopause, has been considered in the present study. A set of dimensionless nonlinear Schrödinger equations has been derived taking into account the finite frequency as well as ion temperature corrections. The dynamical equation of the ion acoustic wave (propagating at an angle with respect to the background magnetic field) in the presence of ponderomotive nonlinearity due to KAW is also derived. Numerical simulation has been carried out to study the effect of nonlinear interaction between these waves which results in the formation of localized structures and turbulent spectrum, applicable to the high-β plasmas like magnetopause regions. Results reveal that due to the nonlinear interplay between these waves, natures of the formation of localized structures are complex and intense in nature in quasi steady state. From the results, we have found that spectral index follows the scaling ∼k À 3=2 ⊥ at large scale and spectral index follows ∼k À 2:80 ⊥ À Á at small scale. We also found the steepening in the turbulent spectrum. Steepening in the turbulence spectrum has been reported by the Time History of Events and Macroscale Interactions during Substorms spacecraft across the magnetopause, and results are found to be consistent with spacecraft observation. RINAWA ET AL.
Energy flux of Alfvén waves in weakly ionized plasma
Astronomy and Astrophysics, 2008
The overshooting convective motions in the solar photosphere are frequently proposed as the source for the excitation of Alfvén waves. However, the photosphere is a) very weakly ionized, and, b) the dynamics of the plasma particles in this region is heavily influenced by the plasma-neutral collisions. The purpose of this work is to check the consequences of these two facts on the above scenario and their effects on the electromagnetic waves. It is shown that the ions and electrons in the photosphere are both un-magnetized; their collision frequency with neutrals is much larger than the gyrofrequency. This implies that eventual Alfvén-type electromagnetic perturbations must involve the neutrals as well. This has the following serious consequences: i) in the presence of perturbations, the whole fluid (plasma + neutrals) moves; ii) the Alfvén velocity includes the total (plasma + neutrals) density and is thus considerably smaller compared to the collision-less case; iii) the perturbed velocity of a unit volume, which now includes both plasma and neutrals, becomes much smaller compared to the ideal (collision-less) case; and iv) the corresponding wave energy flux for the given parameters becomes much smaller compared to the ideal case.
New Regime of Inertial Alfvén Wave Turbulence in the Auroral Ionosphere
2024
We investigate a new regime of inertial Alfvén wave turbulence observed in the very low beta plasma of the auroral ionosphere using electric and magnetic field measurements by the TRICE-2 sounding rocket. Combining the observed features of the electric and magnetic field frequency spectra with the linear properties of inertial Alfvén waves, we deduce the path of the anisotropic turbulent cascade through wave vector space. We find a critically balanced cascade through the magnetohydrodynamic scales of the inertial range down to the perpendicular scale of the plasma skin depth, followed by a parallel cascade to the ion inertial length. We infer damping of the cascade by a combination of proton cyclotron damping and electron Landau damping.
J. Geophys. Res, 2002
1] An analytical and numerical study is made of the influence of plasma finite pressure on the structure of Alfvén waves with large numbers of the azimuthal wave number, m ) 1, as well as of the conditions under which the waves can be poloidally polarized. The study is based on using the axisymmetric model of the magnetosphere assuming the background plasma inhomogeneity along field lines and across magnetic shells, the curvature of field lines, and an equilibrium electric field. The poloidality condition of the mode can imply that in the region where many azimuthal wavelengths fit in the region where the propagation of the wave is possible (the transparent region). The broader is the transparent region, the less stringent conditions are imposed on azimuthal wave numbers of the poloidally polarized Alfvén wave. In this paper it is shown that with nonzero plasma pressure, the transparent region is much broader when compared with cold plasma case. For instance, if finite pressure for the second standing harmonic along a field line of the wave (N = 2) is accounted for, the width of the transparent regions several thousand kilometers, and poloidal Alfvén waves can exist when m ) 10. This is consistent with experimental data on radially polarized Pc4 pulsations in the magnetosphere which have m from 50 to 150, whereas in the case of zero pressure the transparent region does not exceed a few tens of kilometers; therefore, in b = 0 case, poloidally polarized waves must have too large values of m in excess of 1000, which is not observed. A further important result of this study implies that near the ring current maximum there must exist a cavity, and high-m oscillations enclosed within this cavity must be standing oscillations across magnetic shells.
Kinetic Excitation Mechanisms for ION-Cyclotron Kinetic Alfv�n Waves in Sun-Earth ConnectionI
Space Sci Rev, 2003
We study kinetic excitation mechanisms for high-frequency dispersive Alfvén waves in the solar corona, solar wind, and Earth's magnetosphere. The ion-cyclotron and Cherenkov kinetic effects are important for these waves which we call the ion-cyclotron kinetic Alfvén waves (ICKAWs). Ion beams, anisotropic particles distributions and currents provide free energy for the excitation of ICKAWs in space plasmas. As particular examples we consider ICKAW instabilities in the coronal magnetic reconnection events, in the fast solar wind, and in the Earth's magnetopause. Energy conversion and transport initiated by ICKAW instabilities is significant for the whole dynamics of Sun-Earth connection chain, and observations of ICKAW activity could provide a diagnostic/predictive tool in the space environment research.