ULF waves-their relationship to the structure of the Earth's magnetosphere

This is the authors' abstract. We don't add key points for this paper.

The Earth's magnetosphere is highly structured, in terms of both magnetic field and plasma characteristics. This structure has a profound influence on the propagation of plasma waves, especially ultra-low-frequency (ULF) waves with mHz frequencies, which have wavelengths comparable with typical magnetospheric dimensions. The basic theory of ULF hydromagnetic wave propagation in an infinite, homogeneous, uniformly magnetized plasma has been extensively modified to cope with the requirements of applying it to the magnetosphere. The authors consider the field-line-guided Alfven wave modes and the isotropic fast hydromagnetic wave modes, and show how the existence of magnetospheric boundaries can affect the structure of both modes. The magnetosphere can also be considered as a cavity in which fast cavity modes may exist, with frequencies quantized by the three-dimensional cavity shape. Azimuthal variation in a system with radial Alfven speed structure leads to the idea of 'field-line resonance'.