Ionosphere‐magnetosphere coupling: 2. Electric fields

The past 4 years represents an unprecedented period of scientific achievement with regard to advances made in our knowledge of electrodynamic processes acting within the magnetosphere and ionosphere. Perhaps the most impressive accomplishment has been the emergence of conceptual models that include dynamical links between the terrestrial upper atmosphere, the ionosphere, and the magnetosphere. It is now clear that the flow of the magnetized solar wind plasma past the magnetosphere establishes a permanent internal pattern of electric currents connecting the magnetopause with ionospheric regions at the inner peripheries of the auroral ovals. These currents, aligned in narrow longitudinal sheets, close through the ionosphere to create a global pattern of electric fields and currents. It should not be thought that the ionosphere and the upper atmosphere are simply passive receptors of these external influences, however, since they both exert important influences upon the magnetosphere through energy dissipation, variable electrical resistivity, and other processes. As a consequence it is no longer reasonable to consider separately the electrodynamic phenomena of the ionosphere or the magnetosphere. Instead, one must adopt a unified view based upon consideration of the full implications of magnetosphere‐ionosphere‐atmosphere (MIA) couplings and dynamics.