Generation of electromagnetic ion cyclotron waves in the ionosphere by localized transverse dc electric fields

Localized dc electric fields directed perpendicular to the geomagnetic field are studied as a possible ionospheric source of electromagnetic ion cyclotron waves. The eigenvalue formulation of the problem is solved numerically and a class of unstable electromagnetic ion cyclotron eigenmodes are found that have properties consistent with some observations of broadband waves near auroral arcs. The frequency range of instability is comparable to the spectral width measured from photometer observations of broadband auroral flickering. Eigenmodes are associated with electric field polarization reversals and E/B ratios similar to that encountered by satellites and sounding rockets traversing auroral arcs. The dc electric field affects ion resonance conditions and allows for resonant interaction within the extent of the eigenfunction.