Discrete auroral arcs and nonlinear dispersive field line resonances

Dispersive effects in field line resonances (FLRs) are discussed in the con text of potential structures, parallel currents, and auroral density caviti es observed by the FAST satellite. Our model includes the Earth's dipole ma gnetic field, and accounts for electron inertia, electron thermal pressure, finite ion gyroradius effects, and field aligned variations of the plasma density and ambient electron and ion temperatures. For realistic backgound parameters, we show that finite plasma temperature effects determine the dy namics of FLRs and that solitary wave structures evolve out of the resonanc e region, producing deep density cavities above the polar ionospheres. Resu lts are shown to be in reasonable agreement with ground and satellite obser vations, with the exception of the magnitude of low altitude electric field s.