Geomagnetic activity dependence of O in transit from the ionosphere

Energetic O⁺ ions have important dynamic effects on the ring current. Insights into the effects of O⁺ on ring current dynamics have come primarily from models, not observations. Here, we discuss observations of O⁺ populations escaping from the ionosphere and their access to the plasma sheet and ring current. We review data establishing that a significant flux of O⁺ escapes the ionosphere during geomagnetically quiet intervals. We then estimate the relative magnitude of the O⁺ population in transit between the ionosphere and ring current during quiet intervals before geomagnetic storms. Our analysis suggests that dynamic reconfigurations of the magnetosphere during geomagnetic storms significantly alter the O⁺ transport paths from the ionosphere to the ring current. During these reconfigurations some of the pre-existing, quiet time, in-transit O⁺ populations are captured on magnetic field lines leading to the ring current. The prompt appearance of this O⁺ population in the ring current could modify the evolution of the ring current in the storm growth phase. Our analysis suggests that the consequences of an activity-dependent O⁺ transport path to the ring current should be systematically investigated.