Electric double layer caused by a plasma flow along the mirror field

An evolution of a parallel electric field is studied by means of a one-dimensional electrostatic particle simulation model. A parallel plasma flow with initially different pitch angles between electrons and ions is shown to cause an electric field in the mirror field. A large-amplitude electric potential structure is created as a result of a continuous injection of the flow. The scale length of the structure is measured as that of the mirror field rather than the Debye length. The net potential difference increases when the ion bulk flow energy increases. A marked acceleration of passing electrons is observed. The potential difference in the actual magnetospheric environment can exceed 2.5 kV. These results confirmed that a parallel plasma flow which is probably produced by tail reconnections can be responsible for substorm-associated discrete auroras. (author)