Compressional high-m Pc5 ULF waves in the magnetosphere: theoretical considerations

Abstract:

The compressional Pc5 waves with hight azimuthal wave numbers (m>>1) are often observed in the magnetosphere at high level of the geomagnetic activity. The four ULF modes were suggested as a possible explanation of these waves: Alfven ballooning mode, slow magnetosonic mode, drift compressional mode, and drift mirror mode. These modes are considered for the following issues: field aligned structure, transverse structure, generation mechanism, instabilities. Both MHD and kinetic approaches are used. It is concluded that the most probable modes are Alfven ballooning and drift compressional modes coupled with each other. In a gyrokinetic framework, these modes are described by a system of two integro-differential equations. This system takes into account drift-bounce wave-particle interaction, finite plasma pressure, plasma and magnetic field inhomogeneity along field lines and transverse to magnetic shells, and mode coupling due to field line curvature. The conditions of the stablity of these modes and their spatial structure are studied.