Ring Current Ions Measured by the RBSPICE Instrument on the Van Allen Probes Mission

Earth’s ring current has been a subject of interest and considerable study for nearly a century, from the days of ground-based geomagnetism to the satellite era. Protons, helium ions, and oxygen ions are known to contribute to the ring current species population and energy density content, and this is the population that produces equatorialregion depressions in Earth’s magnetic field during large geomagnetic disturbances associated with the Dst index. These ion species are also important in understanding ion transport and charge exchange processes in the inner magnetosphere. However, measurements of such ions are relatively rare. In this paper we report on ion flux measurements of the ring current population made by the Radiation Belt Storm Probe Ion Composition Experiment (RBSPICE) instruments on the National Aeronautics and Space Administration (NASA) Van Allen Probes spacecraft. Proton (45-kiloelectron-volt [keV] to 518-keV), He ion (65-keV to 520-keV), and O ion (140-keV to 1130-keV) integral and differential flux measurements from approximately two years of observations, coving all magnetic local times, are reported. These contemporary data at energies >100-keV are a unique resource that can provide verifications of, and improvements to, models of ring current ion energization and losses in Earth’s magnetosphere, including their roles in plasma processes for producing instabilities and wave generation.