Auroral density fluctuations on dispersive field line resonances

A model is presented that describes the excitation of density perturbations and parallel electric fields by standing shear Alfven waves on dipole fiel ds in Earth's magnetosphere. The model includes the effects of electron ine rtia and gyro-kinetic dispersion, accounting for field-aligned variations o f the electron and ion temperatures and the ambient plasma density. In a mo del dipole magnetosphere, it is found that dispersion and nonlinearity dete rmine the depth, spatial structure, and temporal evolution of large-amplitu de density fluctuations near to the polar ionospheres. The characteristics of magnetospheric density cavities and their relationship to auroral lumino sity, or field-aligned currents, is discussed in the context of recent sate llite and ground based observations.