In situ generation of intense parallel electric fields in the lower ionosphere

The authors look at simple models which could generate intense electric fields, on the order of millivolts per meter in the ionosphere. Such field strenths are implied by a number of different ionospheric observations of electric fields, currents, and plasma waves. They concentrate on the possible existence of quasistatic fields on timescales of electron collision times or the Alfven transit time. They draw conclusions with regard to horizontal gradient scale lengths, namely that 100 m horizontal gradient scales are required, or for longer gradient scales, then return currents are shown to flow along the same paths as precipitating electrons, and hence current densities parallel to field lines are substantially decreased.