By using the full electromagnetic drift kinetic equations for electrons and ions, the general dispersion relation for geodesic acoustic modes (GAMs) is derived incorporating the electromagnetic effects. It is shown that m = 1 harmonic of the GAM mode has a finite electromagnetic component. The electromagnetic corrections appear for finite values of the radial wave numbers and modify the GAM frequency. The effects of plasma pressure βe, the safety factor q, and the temperature ratio τ on GAM dispersion are analyzed.
Using kinetic theory for homogeneous collisionless magnetized plasmas, we present an extended review of the plasma waves and instabilities and discuss the anisotropic response of generalized relativistic dielectric tensor and Onsager symmetry properties for arbitrary distribution functions. In general, we observe that for such plasmas only those electromagnetic modes whose magnetic-field perturbations are perpendicular to the ambient magnetic field, i.e., B1 ⊥ B0, are effected by the anisotropy. However, in oblique propagation all modes do show such anisotropic effects. Considering the non-relativistic bi-Maxwellian distribution and studying the relevant components of the general dielectric tensor under appropriate conditions, we derive the dispersion relations for various modes and instabilities. We show that only the electromagnetic R-and L-waves, those derived from them (i.e., the whistler mode, pure Alfvén mode, firehose instability, and whistler instability), and the O-mode are affected by thermal anisotropies, since they satisfy the required condition B1⊥B0. By contrast, the perpendicularly propagating X-mode and the modes derived from it ( the pure transverse X-mode and Bernstein mode) show no such effect. In general, we note that the thermal anisotropy modifies the parallel propagating modes via the parallel acoustic effect, while it modifies the perpendicular propagating modes via the Larmor-radius effect. In oblique propagation for kinetic Alfvén waves, the thermal anisotropy affects the kinetic regime more than it affects the inertial regime. The generalized fast mode exhibits two distinct acoustic effects, one in the direction parallel to the ambient magnetic field and the other in the direction perpendicular to it. In the fast-mode instability, the magneto-sonic wave causes suppression of the firehose instability. We discuss all these propagation characteristics and present graphic illustrations. The threshold conditions for different instabilities are also obtained.
The dispersion relation for electromagnetic ion cyclotron (EMIC) waves is analyzed for a multi-ion cold plasma. Several cases accounting for the relative contribution of the nitrogen (N + ) and the oxygen (O + ) ions and wave normal angle ( ) are presented. It is found that the presence of N + significantly changes the dispersion properties of EMIC waves, leading to a new frequency band with additional cutoff, crossover, and resonance frequencies just above the oxygen cyclotron frequency (Ω O + ). The method for estimation of ions concentration from cutoff frequencies based on observation is also revisited, and N + concentration is determined. The minimum resonant energy of N + band is also calculated. This new N + band is relevant to reduce the discrepancy in mode detection near Ω O + in the observed wave spectrum in order to quantify the transport and energization of N + , in addition to O + , for their relative contribution to the loss and/or scattering mechanisms.Plain Language Summary EMIC waves are important due to their role in the dynamics of the magnetosphere. The theoretical prediction of a new N + band in EMIC waves has been proposed, which has totally different dispersion properties than O + band and can lead to motivation for finding the possible solution to refine data of current missions with such mass resolution to distinct N + from O + . The observational evidence of low-frequency N + band EMIC waves of this theoretical finding may become possible after the mass resolution. In this letter, we demonstrate that the relative contribution of N + to O + introduces a new N + band and significantly affects the dispersion properties of EMIC waves.
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