Relationship between Region 2 field-aligned current and the ring current: Model results

[ 1] Detailed investigations on the relationship between the ring current and Region 2 field-aligned currents ( FACs) have been tenuous. Using the Comprehensive Ring Current Model ( CRCM), we first studied their relationship for two GEM storm events ( 22 April 2001 and 21 October 2001) through model and data comparison. The simulated Region 2 FACs for two different magnetic storm events capture major characteristics of the Iridium measurements, and the simulated ENA flux has a reasonable agreement with the IMAGE/HENA data. We then examined the effects of polar cap potential drop, ionospheric conductivity, plasma sheet density and different magnetic field models on the development of Region 2 FACs, and the relationship between Region 2 FACs and the ring current, either through one of the two GEM events or the 12 August 2000 storm. It is shown that an increase in polar cap potential, ionospheric conductivity, or plasma sheet density generally results in an increase in Region 2 FACs' intensity, but Region 2 FACs display different local time and latitudinal distributions for changes in each parameter due to the different mechanisms involved. The CRCM run in the Tsyganenko 2004 magnetic field model for storm times ( T04S), which includes a partial ring current, produces the dawn-dusk asymmetry in Region 2 FACs during geomagnetically active times, as reported by Anderson et al. ( 2005): more intense currents flow into the ionosphere around dusk, compared to those that flow out of the ionosphere around dawn, and the dusk currents shift further equatorward than do the dawn currents.