Outer Ring Current Energetic N+1 and O+1: Solar Cycle and Geomagnetic Variations and Relation to Topside Ionosphere Ion Densities

We use the Geotail/EPIC/STICS ion mass spectrometer to study 10-210 keV/e O+1 and N+1 flux in the outer ring current (ORC) at 9-15 Re. We find that average N+1/O+1 ratios (N/O) in the afternoon MLT sector vary by a factor of 2 over a solar cycle, from 40% at solar minimum to 20% at solar maximum. Individual 2-6 hr N/O samples range from 0.15 (moderate solar maximum storm) to 1 (18-hr solar minimum superquiet interval). Ionospheric origin O+1 and N+1 are known to be important ring current ions in great magnetic storms. We find that N+1 is the third most important ORC ion after H+ and O+1 during some moderate storms (Dstmin is about -80 nT) at both solar minimum and solar maximum. We use high-latitude topside ionospheric AE-D/MIMS and OGO-6 ion composition data as a baseline reference to investigate whether ORC N/O variations may be related to topside ionospheric density N/O spatial variations.