[PEM16-P14] Oxygen impulsive energization during the storm main phase and its contribution to the ring current buildup
Keywords:Magnetic storms, Ring current, Oxygen ion outflow, Plasma transport and acceleration
Van Allen Probes observed oxygen ion enhancements during the main phase of the 17 March 2015 storm. The oxygen energy density showed different temporal variations and radial profile from the proton energy density. It was enhanced during the early main phase (Dst ~ -120 nT) up to the proton energy density level in an L range of 3 to 5. However, it decreased by about an order of magnitude around the beginning of the later main phase. It was increased again during the later phase (Dst ~ -220 nT) particularly at L ~ 3, while it did not reach the early phase level. The radial profile was affected by temporarily impulsive enhancements more significantly than the proton energy density. The difference between the outbound (pre-midnight) and inbound (around midnight) paths is much clearer for oxygen ions than protons.
In this poster, we show the results of multi-event studies on such mass-dependent features during magnetic storms that occurred in 2013 to 2016. Our analysis is particularly focused on changes of energy spectra and pitch angle distributions, and spatial distributions of the oxygen ion contribution to the ring current. We discuss when and where ionospheric oxygen ions are energized to make a significant contribution to the ring current.