Monopolar and bipolar auroral electric fields and their ionospheric signature

J. De Keyser, R. Maggiolo, and M. Echim
Belgian Institute for Space Aeronomy

Most of the quasi-static high-altitude auroral electric fields observed by
CLUSTER can be classified into monopolar and bipolar structures. The
observations show that monopolar electric fields tend to be associated with
polar cap boundary arcs, while bipolar fields are linked to discrete arcs
within the auroral oval. We propose an explanation of this association in terms 
of a simple model of the overall configuration of the magnetotail and the 
results of kinetic model computations. We propose quasi-electrostatic models of 
the magnetosphere-ionosphere coupling that describe the auroral current system 
associated with such high-altitude fields. These models give indications about 
the location of up- and downward field-aligned current regions, the ionospheric 
and magnetospheric convection along the arc, the acceleration or deceleration 
of precipitating particles, and the behaviour of escaping ionospheric ions.