Field line resonance interference model for multiple auroral arc generation

A simple model for the generation of poleward moving multiple amoral struct ures in the nightside ionosphere is described. The model is based upon the premise that field line resonance oscillations are responsible for amoral a re generation. The auroral structures are considered to be a result of inte rference between Alfven field line resonance oscillations on different L sh ells. Because of the dependence of the Alfven resonance frequency on L shel l, any two neighboring L shells which oscillated initially with the same ph ase, after some time appear to be in opposite phase. That results in the ap pearance of counter-directed electric fields at these L shells and a large field-aligned current between them, which can produce the electron accelera tion along the magnetic field and be responsible for auroral are generation . The out of phasing between the oscillating L shells begins first at low l atitudes and then propagates poleward producing poleward moving amoral arcs . The model requires that oscillations be maintained for many cycles of the waves and the source for energy is ultimately derived from magnetospheric convection in the plasma sheet. The field line resonance interference model explains periodic behavior in such auroral activity having frequencies in the Pc5 range. It is significant that the period of oscillation may be grea ter than that for the Alfven resonant oscillations, which implies that two separate frequencies may appear on the same field line. The poleward propag ation of the amoral arcs in this model is a result of the poleward propagat ion of interference maxima rather than any real plasma or wave propagation.