Ionospheric Currents and Their Coupling to the Magnetosphere

Abstract:

Electric currents play an important role in the energy coupling between the magnetosphere and ionosphere. The interaction of the solar wind with the magnetosphere forces plasmas into a global circulation or convection in the magnetosphere and the magnetically connected ionosphere. The energy and momentum transfer from the magnetosphere to the ionosphere is associated with magnetic field-aligned currents. The field-aligned currents flow into and out of the high-latitude ionosphere, and are closed by horizontal current, primarily the Pedersen current. It is through such a process that the ionosphere is forced into the convective motion at high latitudes and by which the power generated by the solar wind-magnetosphere dynamo is partly dissipated into the ionosphere-thermosphere system. At middle and low latitudes the ionospheric wind dynamo becomes the dominant generator of ionospheric currents, which operates when the atmospheric neutral winds, via ion-neutral collisions, cause ions and electrons to move at different velocities across Earth’s magnetic field. This paper presents a brief overview of the generation mechanisms of ionospheric currents at high latitudes as well as in the mid- and low-latitude regions. The utility of the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) is demonstrated in obtaining the large-scale ionospheric horizontal currents and the associated field-aligned current in the high-latitude polar regions based on various ground- and space-based observations. The distributions of ionospheric currents at mid and low latitudes are illustrated using the Thermosphere-Ionosphere-Electrodynamic General Circulation Model (TIEGCM). Examples of the global ionospheric current system under both geomagnetically quiet and active times will be shown.