抄録
A. Schmidt surmised in 1924 that geomagnetic storms caused the build up of an external ring current. Ever since, there have been speculations about the nature of the responsible mechanisms. Direct observations of plasma injection into closed field line regions of the Earth's magnetosphere have sparked renewed interest in the associated physical processes. Most of the early models of plasma injection involved the formation of large scale electric fields that were constrained to be perpendicular to the magnetic field and to be derivable from a potential. Electric fields of this character clearly play an important role, but both data and theory now indicate that parallel electric field components, inductive electric fields, and electric fields associated with waves also play important roles. These particle injection processes are closely related to those responsible for the acceleration of particles into the auroral ionosphere. Attempts at modelling the time dependent magnetic and electric fields to help understand these processes have met with difficulties that highlight the need for multi-spacecraft measurements in the 6 the 12 Re region of the magnetotail.
