The flywheel effect: Ionospheric currents after a geomagnetic storm

In the period following a geomagnetic storm the high‐latitude, magnetospheric‐driven convection pattern is normally weak. However, the neutral circulation, set up by ion‐neutral momentum coupling during the main phase of the storm, may continue for several hours after the storm has ended. This persistent neutral circulation has the potential to drive Hall currents for some hours. In this paper we investigate these “flywheel” currents by simulating a storm which occurred on the 23^rd of November 1982 using the National Center for Atmospheric Research Thermosphere Ionosphere General Circulation Model (NCAR‐TIGCM). The resulting high‐latitude, height‐integrated Hall currents are dominated by the neutral‐wind‐driven component for several hours after the end of main phase of the storm. The direction of these currents is reversed from normal. Analysis of the neutral and ion components of this current system indicates that the neutral component may drive as much as 80% of the high‐latitude current system immediately after the storm has ended, and may continue to dominate this system for 4 to 5 hours.