Electron dropout echoes induced by interplanetary shock: A statistical study. Issue 8 (3rd August 2017) - Liu, Z. Y.
Abstract: "Electron dropout echo" as indicated by repeated moderate dropout and recovery signatures of the flux of energetic electron in the outer radiation belt region has been investigated systematically. The electron moderate dropout and its echoes are usually found for higher‐energy (>300 keV) channel fluxes, whereas the flux enhancements are obvious for lower energy electrons simultaneously after the interplanetary shock arrives at the Earth's geosynchronous orbit. The electron dropout echo events are found to be usually associated with the interplanetary shocks arrival. The 104 dropout echo events have been found from 215 interplanetary shock events from 1998 to 2007 based on the Los Alamos National Laboratory satellite data. In analogy to substorm injections, these 104 events could be naturally divided into two categories: dispersionless (49 events) or dispersive (55 events) according to the energy dispersion of the initial dropout. It is found that locations of dispersionless events are distributed mainly in the duskside magnetosphere. Further, the obtained locations derived from dispersive events with the time‐of‐flight technique of the initial dropout regions are mainly located at the duskside as well. Statistical studies have shown that the effect of shock normal, interplanetary magnetic field B z and solar wind dynamic pressure may be insignificant to these electron dropout events. We suggest that the ∼1 min electric field impulse induced by the interplanetary shock produces a more pronounced inward migration of electrons at the duskside, resulting in the observed duskside moderate dropout of electron flux and its consequent echoes. Key Points: Electron dropout echo events (104 cases) in the outer radiation belt have been found from interplanetary shock events (215 cases) Statistical study indicates the response of magnetosphere to interplanetary shock is strongly dawn‐dusk asymmetric Shock‐induced electric field impulse drives stronger inward migration of relativistic electrons at duskside, which forms dropout echoes