Relationship of the ring current plasma pressure from ENA images and field-aligned currents

The steady state MHD force balance equation and current continuity show that pressure gradients in the equatorial ring current are associated with field-aligned currents (FAC) for large spatial and slow temporal scale changes of the magnetic field. To obtain the ring current pressure, ion distributions are inverted from ENA images obtained by IMAGE/HENA and MENA and used to calculate the plasma density, temperature, and pressure for a series of geomagnetic storms/substorms on 22 January, 12 February, 9 and 10 March, 29 May, 23 September and 13 October in 2004. FAC patterns in the high-latitude ionosphere are derived from the Weimer 2005 FAC model with time shifted solar wind and IMF driven input parameters. Comparing the ring current pressure with the field-aligned current pattern mapped to the equator shows the dynamics of the relationship between the plasma pressure/pressure gradients and field-aligned currents for the series of storms/substorms addressed in this presentation.