Current-voltage relationship including plasma flow along the mirror field

Abstract

lt is commonly believed that field-aligned currents ( currents parallel to the magnetic field ) are carried by electrons, which are more mobile than ions. Contrary to this common view, it is shown that, based on a collisionless model, even for V0 ＜＜ νTe, where V0 is the field-aligned plasma flow speed and νTe is the electron thermal speed, plasma sheet ions can carry a net downward field-aligned current into the ionosphere when an earthward plasma flow is injected at the plasma sheet into the mirror field. This is simply due to different pitch angle distributions of ions and electrons at the plasma sheet caused by the plasma flow. Relevance of this possibility to downward fleld-aligned currents observed poleward of the evening auroral zone is discussed.