Magnetosphere‐ionosphere coupling

A simple two‐dimensional model of the magnetosphere‐ionosphere system is discussed in which a localized electromotive force applied across a magnetic field line at t =0 is shown to propagate along the magnetic field with the Alfvén velocity. The perpendicular electric field is assumed to reverse direction across the field line. Since the perpendicular electric field is limited in space, the propagation involves parallel electric fields whose magnitude depends on the characteristic scale length of the applied emf and the local plasma parameters. The electric field pulse associated with the ‘shock’ front is reflected at the ionosphere and propagates back to the source region. The finite Pedersen conductivity in the ionosphere damps the wave, and a steady state current system is established in the order of several hours. The parallel electric field can accelerate ions and electrons.