Origins of energetic ions in the cusp

Abstract

Recent studies reported on a new magnetospheric phenomenon called cusp energetic particle (CEP) events. It has been suggested that these energetic particles with significant fluxes up to several hundred keV/e are accelerated locally in the cusp. An alternative explanation for the energetic particle events is that they are accelerated at the quasi‐parallel bow shock, then transported downstream and enter the cusp along newly reconnected field lines or some other solar wind entry mechanism. It is well known that shock‐accelerated ions have characteristic abundance ratios, composition ratios relative to the solar wind composition, temperatures, and spectral dependency on solar wind conditions. These parameters are used to distinguish between a local (cusp) and remote (bow shock) acceleration. Our results show that average values of these parameters in the cusp are comparable to those at quasi‐parallel shocks. Furthermore, changes in some of these parameters indicate a solar wind entry process that depends on energy and mass. No local acceleration is required to explain the observed CEP events up to 150 keV/e. For ions above 150 keV/e the magnetosphere itself may be responsible for the observed cusp fluxes.