Energetic ion variations during substorm intervals using the Van Allen Probes data

Abstract

The study investigates ion flux variations for the substorms in the inner magnetosphere. The effect of substorm-induced magnetic field dipolarization on the O+ and H+ ion flux is analysed for 22 events from the year 2018 using the Helium, Oxygen, Proton, and Electron (HOPE) Mass Spectrometer data on board the Van Allen Probes (VAP/RBSP) satellite. The clear dipolarization signatures are observed using the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) suite from the VAP. These observations provide evidence of the ion flux enhancement at 1–50 keV energy after the substorm onset, in particular, the energy range of 20–50 shows dominance. The typical characteristics of magnetic field dipolarization and its time scales are investigated. It is found that the O+ ion flux enhances greater in magnitude than H+ ion flux at energies 20–50 keV after the substorm onset. In addition to it, the correlation of these enhanced oxygen fluxes with the related interplanetary magnetic field (IMF) Bz, solar wind velocity (Vsw), and the auroral electrojet (AE) index are found good. The new results reports that the ion flux variation ratio shows the MLT dependence for different energy ranges and found that the peak of the O+/ H+ ion flux ratio centred near midnight for the energy range of 8–20 keV, whereas the O+/ H+ ion flux ratio of the energy 20–50 keV is high within the post-midnight. The possible mechanisms for the enhanced ion flux are discussed.