Heating of the magnetospheric plasma by electromagnetic waves generated in the magnetosheath

After entering the magnetosphere, electromagnetic waves excited in the magnetosheath are absorbed by the magnetospheric plasma either through cyclotron damping at harmonics of the proton and electron gyrofrequencies or through an encounter with the upper hybrid resonance. This absorption of wave energy causes the plasma to be heated. Since the magnetosphere is an inhomogeneous medium for the propagation of ordinary and extraordinary waves, absorption takes place at a spatial location that depends on the wave frequency. An analysis of the passband of extraordinary waves shows that protons are heated rather uniformly throughout the magnetosphere because of cyclotron damping, whereas electrons are most efficiently heated at the plasmapause by wave absorption at the upper hybrid resonance. Results of recent observations of low-frequency electric fields indicate that 100-kev protons can be produced by this mechanism.