This paper presents results from a fully self-consistent kinetic particle simulation of the time dependent formation of large scale parallel electric fields in the auroral zone. The results show that magnetic mirroring of hot plasma that streams earthward from the magnetotail leads to a charge separation potential drop of many kilovolts over an altitude range of a few thousand kilometers. Once the potential drop is formed it remains relatively static and is maintained in time by the constant input of hot plasma from the tail; the parallel electric field accelerates ions away from Earth and ionospheric electrons towards the Earth. At altitudes above where the ions are mirror reflected and accelerated by the parallel electric field, low frequency waves are generated, possibly due to an ion/ion two-stream interaction. ¿ American Geophysical Union 1993