DYNAMICS OF THE GENERATION OF MAGNETIC-FIELD-ALIGNED ELECTRIC-FIELDS BY DRIFT CURRENTS

A study is made of the process of generation and evolution of parallel electric fields on closed geomagnetic field lines. Charge separation that is due to the different character of the drift of energetic elect rons and protons of inhomogeneous magnetospheric plasma in the geomagn etic field is considered to be the factor responsible for the generati on of the electric field. In a magnetic flux tube that drifts together with the cold plasma, this separation of charges is manifested as the injection of energetic electrons or protons. A numerical self-consist ent calculation of the evolution of the distribution functions of part icles and of the parallel electric field is carried out for the inject ion of energetic electrons into the geomagnetic flux tube. An analytic al investigation of the macroscopic and microscopic processes accompan ying such injection is carried out. The calculations take into account cold ionospheric particles and energetic magnetospheric protons and e lectrons. It was found that an intense parallel electric field is prod uced in the form of two collisionless rarefaction shock waves that sep arate from the equatorial plane in the northward and southward directi ons. Below the front of each shock wave, there is mainly the ionospher ic plasma, while behind the front there are the upward accelerated ion ospheric ions and the hot magnetospheric plasma. Microscopic structure behind the shock front is formed by electrostatic oscillations of a l arge amplitude. Generation conditions for intense longitudinal fields are formulated: The difference in densities of injected energetic elec trons and protons near the equatorial plane must exceed the initial de nsity of cold particles, and the current-associated velocity of cold e lectrons must be larger than the ion sound velocity. It is shown that these conditions can be satisfied, owing to a drift mechanism of charg e separation. A rarefaction shock wave is excited with substantially s maller field-aligned currents as compared with anomalous resistance or double layers. The observed manifestations of the rarefaction shock w aves are auroral plasma cavities.