Solar cycle and geomagnetic N⁺¹/O⁺¹ variation in outer dayside magnetosphere: Possible relation to topside ionosphere

O +1 and N +1 are important ring current ions in great magnetic storms. We study ∼10–210 keV/e O +1 and N +1 in dayside outer ring current (ORC) at ∼9–15 R E using Geotail's EPIC/STICS ion spectrometer. We find: average N +1 /O +1 (Γ N/O ) varies by ∼2 over a solar cycle, ∼40% (∼20%) at solar minimum (maximum); individual Γ N/O values range from ∼0.15 (moderate solar maximum storm) to ∼1 (18‐hr solar minimum superquiet interval); and N +1 is third in importance after H + and O +1 during two moderate storms (Dst min ∼ −80 nT, ∼25% great storm intensity), one at minimum, one maximum. High‐latitude topside ionospheric AE‐D/MIMS ion composition data form a baseline reference used to argue that ORC Γ N/O variations generally reflect and may be partially explained by topside ionospheric density Γ N/O spatial variations.