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. Copyright 2001 by the American Geophysical Union.