Characteristics of storm time ion composition in the near-Earth plasma sheet using Geotail and RBSP measurements

Abstract

Solar wind particles and ionospheric O+ ions infuence the near-Earth plasma sheet and inner magnetospheric composition. We studied the behavior of H+, O+ and He+ ions (9–210 keV) for intense and moderate geomagnetic storms of solar cycle 23 and 24. An average energy density <ε> of ions over a given interval and fux enhancement is estimated using observations from satellites at diferent L values, namely STICS sensor on-board Geotail spacecraft and HOPE spectrometer on-board Radiation Belt Storm Probes. It provides a comprehensive understanding of the energy density variation of H+, O+ and He+ ions with the strength of IMF Bz, Psw, intensity of storms and L value. Statistically, we observed that (1) In the plasma sheet region, during main phase of the intense geomagnetic storm, <εO+/H+> and <εHe+/H+> enhances, (2) <εO+/H+> is well correlated with Psw (CC=0.86) and IMF Bz (CC=0.85), (3) <εO+/H+> shows higher correlation (CC=0.73) with Kp than <εHe+/H+> (CC=0.65), indicating a fairly good dependence on the strength of geomagnetic activity, (4) <εO+/H+> and <εHe+/H+> dependence on L value indicates that O+/H+ and He+/H+ is more pronounced near L=3. It is a cumulative extension of the previous studies on ion composition change which is in accordance with the existing picture of the plasma sheet and inner magnetosphere.