Theory of azimuthally small-scale hydromagnetic waves in the axisymmetric magnetosphere with finite plasma pressure

Abstract

Abstract. The structure of monochromatic MHD-waves with large azimuthal wave number m ) 1 in a twodimensional model of the magnetosphere has been investigated. A joint action of the ®eld line curvature, ®nite plasma pressure, and transversal equilibrium current leads to the phenomenon that waves, standing along the ®eld lines, are travelling across the magnetic shells. The wave propagation region, the transparency region, is bounded by the poloidal magnetic surface on one side and by the resonance surface on the other. In their meaning these surfaces correspond to the usual and singular turning points in the WKB-approximation, respectively. The wave is excited near the poloidal surface and propagates toward the resonance surface where it is totally absorbed due to the ionospheric dissipation. There are two transparency regions in a ®nite-beta magnetosphere, one of them corresponds to the Alfve n mode and the other to the slow magnetosound mode.

Spatio-temporal structure of a poloidal Alfvén wave detected by Cluster adjacent to the dayside plasmapause

“…While the toroidal eigenfrequency T is calculated from the travel time of an Alfvén wave along the field line (Warner and Orr, 1979), P is additionally affected by field line curvature (e.g. Mazur, 1990, 1993), finite plasma β and external currents, such as the ring current (Klimushkin, 1998b;. The spatial and temporal properties of a poloidal wave field are affected by the difference between the field line eigenfrequencies, P and T .…”

Axisymmetric Alfvén resonances in a multi-component plasma at finite ion gyrofrequency

“…It is important to note that this standing wave pattern appears at any wave frequency, and thus is it not associated with any quantization condition of the frequency ω or any other value. In the ω/ω ci =0 case an oscillatory structure arises when the field line curvature (Leonovich and Mazur, 1993;Klimushkin, 1998) or the magnetic field shear are taken into account, but in these cases the wave is travelling rather than standing across magnetic shells.…”

Standing Alfvén waves with m ≫ 1 in an axisymmetric magnetosphere excited by a non-stationary source

“…After that, in the process of their propagation across magnetic shells, they transfer to toroidal oscillations at the expense of their transverse dispersion. At the same time, toroidal oscillations, such as ®eld line resonance, do nothing but enhance their toroidal character in the process of propagation across magnetic shells (see Leonovich and Mazur, 1989). Hence the probability of observation of poloidal oscillations is signi®cantly lower compared to toroidal oscillations.…”