Introduction to the topology of magnetospheric current systems

A brief history of the observations and study of the major magnetospheric current systems is presented. These currents are usually inferred from the observation of their associated magnetic fields but are formed by magnetospheric plasmas. Although the energy sources for the magnetopause and ring currents are well understood, the particle and energy sources for the tail and Birkeland currents are still being sought. It is suggested that the direct entry of magnetosheath plasma into the magnetosphere is responsible for the tail and Region 1 Birkeland currents. 51 references