Contrasting behavior of dipolarization-related electron and ion injections inside GEO
Abstract
A recent study by Motoba et al. (2018, hereafter Paper 1) demonstrated the statistical characteristics of the responses of different ion species to local magnetic dipolarization inside geosynchronous orbit (GEO), using the ion species data from Van Allen Probes observations in 2012-2016. This study, newly adding the electron data, expands Paper 1 primarily to differentiate between the dipolarization-related energetic ion and electron behaviors inside GEO. Using the 144 dipolarization events identified in Paper 1, we have conducted a superposed epoch analysis of 1-1000 keV electrons in the same manner as that made in Paper 1 and contrasted the post-/pre-onset flux ratio of electrons with that of hydrogen ions. Both electron and ion fluxes increase or decrease depending on the energy. On average, the flux ratio peaks at 30 keV for electrons and at 130-160 keV for ions. The energy demarcating flux ratio increase/decrease is a few keV for electrons, which is lower than for ions ( 50 keV). The demarcation energy for electrons is higher in postmidnight than premidnight, which is opposite to that for ions. The different dawn-dusk asymmetries between electrons and ions could be interpreted in terms of their asymmetric pre-onset background energy spectra, being harder (softer) in postmidnight than premidnight for electrons (ions). The initial rise of the electron fluxes lags behind that of the ion fluxes by 1 min, which resembles their behavior at dipolarization fronts in the near-Earth tail. Whereas the ion flux enhancement decays rapidly, the electron flux enhancement lasts over 10 min and has several peaks. The multiple electron flux enhancements may be associated with fluctuating electromagnetic fields that are often superimposed upon the large-scale magnetic field reconfiguration. For sharp dipolarizations both electron and ion energy spectra become harder, which implies that accompanying electric field efficiently influences their transportation and/or energization.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMSM51D2767M
- Keywords:
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- 2730 Magnetosphere: inner;
- MAGNETOSPHERIC PHYSICSDE: 2736 Magnetosphere/ionosphere interactions;
- MAGNETOSPHERIC PHYSICSDE: 2740 Magnetospheric configuration and dynamics;
- MAGNETOSPHERIC PHYSICSDE: 2788 Magnetic storms and substorms;
- MAGNETOSPHERIC PHYSICS