Temporal and Spatial Evolution of Cold Ions in the Inner Magnetosphere During Large Magnetic Storms

To examine the temporal and spatial evolution of cold ions within the inner magnetosphere during geomagnetic storms, we conducted superposed epoch analyses on the electron density (N e ) and the partial ion densities of H + , He + , and O + within the instrument frame energy range of 1–10 eV, using data obtained from the Van Allen Probes. The analyses were performed on a set of 14 large storms (SYM‐H < −100 nT) over a 5‐year period from 2013 to 2017. We found that the electron density and cold H + and He + densities outside the plasmasphere decrease as large storms develop. However, the cold O + density outside the plasmasphere remains largely unchanged during the storm's main and early recovery phases. Based on these observations, we suggest that the less‐dense cold population outside the plasmasphere during storm activities contains more cold O + ions.