Magnetosonic resonances in the magnetospheric plasma

Abstract

A problem of coupling between fast and slow magnetosonic waves in Earth's magnetosphere (magnetosonic resonance) is examined. Propagation both slow magnetosonic wave and Alfven wave can easily be canalized along the magnetic field line direction. The main difference between the two is that slow magnetosonic waves dissipate strongly due to their interaction with the background plasma ions, whose temperature is above the electron temperature. In Earth's magnetosphere, however, there is a region where the dissipation of slow magnetosonic waves can be weak-the inner plasmasphere. The slow magnetosonic waves generated there can be registered directly. In other regions, with strong dissipation of slow magnetosonic waves, their signature may be detected through their impact on the Alfven resonance at frequencies for which the resonant Alfven and slow magnetosonic waves exist simultaneously in the magnetosphere. Owing to their strong coupling with the background plasma ions, resonant slow magnetosonic waves can transfer the energy and impulse from the solar wind to the magnetospheric plasma ions via fast magnetosonic waves penetrating into the tail lobes. A problem of resonant conversion of fast magnetosonic waves into slow magnetosonic oscillations in a magnetosphere with dipole-like magnetic field is also examined.

Experimental evidence of drift compressional waves in the magnetosphere: An Ekaterinburg coherent decameter radar case study

“…The MHD mode with the frequency lower than the Alfvénic is the slow magnetoacoustic mode. However, the slow‐mode frequency is even too small, being 2 orders lower than the Alfvénic [e.g., Leonovich and Kozlov , ]. Moreover, the very validity of the MHD approach in collisionless plasma for the sub‐Alfvénic frequencies has cast doubt because for these frequencies the particle bounce motion must be taken into account which can be done correctly in kinetics only [e.g., Hurricane et al , ].…”

“…There is no agreement on the physical nature of these pulsations. In terms of MHD theory, it seems natural to identify them with the longest‐period MHD mode, the slow magnetoacoustic modes [e.g., Leonovich and Kozlov , ]. However, it is not clear whether the MHD approach is valid for the oscillations with frequencies much below the Alfvénic range in the collisionless plasma because for these frequencies the particle bounce motion must be taken into account which can be done correctly in kinetics only [e.g., Hurricane et al , ].…”

Kelvin‐Helmholtz Instability in the Geotail Low‐Latitude Boundary Layer

“…The growth rate of unstable oscillations in magnetospheric models with a smooth boundary is smaller than in models with a sharp boundary. Moreover, resonance surfaces appear in the boundary layer for the Alfvén and slow magnetosonic (SMS) waves (see Chen & Hasegawa, 1974;Leonovich & Kozlov, 2013;Southwood, 1974). Here the energy of unstable fast magnetosonic (FMS) waves generated by the magnetopause shear flow is absorbed (Klimushkin et al, 2004;Leonovich & Mazur, 1989).…”

“…In this paper we consider the Kelvin-Helmholtz instability in the low-latitude boundary layer (LLBL) of the geotail using its cylindrical model. A similar problem was solved in Leonovich et al (2018) in a model with a boundary having the form of a tangential discontinuity. Here we will consider a magnetosphere model with the boundary in the form of a smooth boundary layer of finite thickness.…”

The Alfvén mode gyrokinetic equation in finite‐pressure magnetospheric plasma

“…In the MHD treatment, the Alfvén wave is coupled with the slow mode [ Walker , ; Klimushkin , ; Mazur et al , ]. This problem can be avoided if it is taken into account that the Alfvén mode usually has much shorter period than the slow mode [ Cheng et al , ; Leonovich and Kozlov , ]. Then, the correct Alfvén mode equation ought to be derived.…”