P. N. Mager

On the ballooning instability of the coupled Alfvén and drift compressional modes

The paper examines the ballooning instability in gyrokinetic approximation taking into account the effects of finite-β, magnetic field line curvature, and diamagnetic drift. We used a simple model with a constant curvature of magnetic field lines which enabled us to obtain analytical results. The possible plasma oscillatory modes comprise the poloidal Alfvén and drift compressional modes, coupled due to the magnetic field line curvature and plasma inhomogeneity. The frequencies of these modes depend on the westward current value. As this value grows, the frequencies of these two branches approach to each other, and the branches are merged at some critical value of the current. Then an instability develops which is called the drift ballooning coupling instability. There are three major differences of the drift ballooning coupling instability from the ordinary MHD ballooning instability: (1) the drift ballooning coupling instability is not aperiodic, there is a real part of the oscillation frequency of the order of the drift frequency, (2) only the mode with the same direction of the azimuthal phase speed as the velocity of the ion diamagnetic drift can be unstable, (3) the instability threshold depends on the diamagnetic drift frequency.

Giant pulsations as modes of a transverse Alfvénic resonator on the plasmapause

The paper assumes that the giant pulsations are oscillations trapped within a resonator resulting from finite plasma pressure on the outer edge of the plasmapause. This resonator is bounded, across the L-shells, by two turning points allowing the wave energy to be channeled azimuthally. This assumption can explain the basic properties of the giant pulsations: strong localization across magnetic shells, poloidal polarization, presence of a significant compressional component in the Pg magnetic field, the fact that their frequency does not depend on the radial coordinate. The wave field structure both across the L-shells and along the field lines is studied. In order to explain the amplitude modulation it is sufficient to suppose that the resonator is excited by some non-stationary process. Generation by a moving source comprised of substorm-injected particles is considered.

Generation of Alfvén Waves by a Plasma Inhomogeneity Moving in the Earth's Magnetosphere

The generation of an Alfvén wave by an azimuthally drifting cloud of high-energy particles injected in the Earth’s magnetosphere is studied analytically. In contrast to the previous studies where the generation mechanisms associated with the resonant wave-particle interaction were considered, a nonresonant mechanism is investigated in which the wave is excited by the alternating current produced by drifting particles. It is shown that, at a point with a given azimuthal coordinate, a poloidally polarized wave, in which the magnetic field lines oscillate predominantly in the radial direction, is excited immediately after the passage of the particle cloud through this point. As the cloud moves away from that point, the wave polarization becomes toroidal (the magnetic field lines oscillate predominantly in the azimuthal direction). The azimuthal wavenumber m is defined as the ratio of the wave eigenfrequency to the angular velocity of the cloud (the drift velocity of the particles). It is shown that the amplitudes of the waves so generated are close to those obtained under realistic assumptions about the density and energy of the particles.

The Alfvén mode gyrokinetic equation in finite-pressure magnetospheric plasma

The paper is concerned with the derivation of the Alfven mode equation in finite-pressure space plasma in gyrokinetic approach. The long plasma approximation is used, where the bounce frequency is much lower than both wave and drift frequencies. The only ultralow frequency mode in the long plasma approximation is the Alfven-ballooning compressional mode, which is described by the Alfvenic dispersion relation with some additional (ballooning) terms caused by the field line curvature and plasma pressure effects. Due to these effects the Alfven mode acquires also considerable parallel magnetic field component. The long plasma approximation allowed us to consider the correspondence between the gyrokinetic and MHD approaches for the Alfven mode equation. It is shown that in 0 < β ≪ 1 case, MHD approach gives correct Alfven wave description, where β is plasma to magnetic pressure ratio.

The structure of low-frequency standing Alfvén waves in the box model of the magnetosphere with magnetic field shear

The paper is concerned with the influence of magnetic field shear on the structure of Alfven waves standing along field lines in the one-dimensionally inhomogeneous box model of the magnetosphere, enclosed between two parallel, infinitely conducting planes (ionospheres). We consider the transverse small-scale Alfven waves whose azimuthal component of the wave vector

On the structure of azimuthally small-scale ulf oscillations of a hot space plasma in a curved magnetic field: Modes with discrete spectra

k_y

Multiradar observations of substorm-driven ULF waves

satisfies the condition

Experimental evidence for the existence of monochromatic transverse small‐scale standing Alfvén waves with spatially dependent polarization

k_y l\,{\gg}\,1

Correspondence between the ULF wave power spatial distribution and auroral oval boundaries

, where

Propagation of MHD Waves in a Plasma in a Sheared Magnetic Field with Straight Field Lines

l