Global Resonant MHD Waves in the Magnetosphere

A major shortcoming of theories of long-period magnetic pulsations is the separate treatment of the problems of wave excitation and resonant coupling. This could account for many substantial discrepancies between the waveguide/cavity theories and observations. A unified approach leading to a new type of field line resonance (FLR) excitation mechanism is presented. It is shown that in a steady state the direct coupling of the waveguide modes to the local field line oscillations provides a natural and a very efficient transport of energy from the magnetosheath flow to the shear Alfv´en waves even in the ideal MHD limit. Many well-known observational features are recovered.