The effects of the location and the timing of local convection electric field enhancements in the formation of ion multiple-nose structures

Abstract

We investigate the formation of He+ and O+ multiple-nose structures observed by the Helium, Oxygen, Proton, and Electron instrument onboard Van Allen Probes A on December 2, 2012. Previous studies have suggested that multiple-nose structures can be formed by changes in the convection electric field. However, the specifics of how these changes can produce multiple-nose structures have been left unresolved. In this study, we simulate ions as they drift from the plasma sheet into the inner magnetosphere and find that the multiple-nose structures were created by the overlap of a nose structure and a spectral gap in the energy-time spectrograms of the measured ion fluxes. Ion drift path tracings show that the spectral gap was produced by an enhancement of the convection electric field several hours before. Furthermore, the simulations reveal new insight of how the timing and location of the local electric field enhancements play a key role in the formation of the observed multiple noses.