Magnetosphere‐ionosphere coupling

TLDR

In the magnetosphere‑ionosphere system the perpendicular electric field reverses across a field line, and the resulting parallel electric field can accelerate ions and electrons. The study presents a simple two‑dimensional model to examine how a localized electromotive force applied across a magnetic field line propagates along the field at the Alfvén velocity. The model assumes a spatially limited perpendicular electric field, leading to parallel electric fields whose magnitude depends on the emf scale length and local plasma parameters, and the disturbance propagates along the field at the Alfvén speed. The shock‑front electric field pulse reflects at the ionosphere, propagates back to the source, and is damped by finite Pedersen conductivity, leading to a steady‑state current system within several hours.

Abstract

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.