Cusp Energetic Ions: A Bow Shock Source.
S. W. Chang, J. D. Scudder, S. A. Fuselier, J. F. Fennell, K. J. Trattner · 1998
Recent interpretations of cusp energetic ions observed by the POLAR spacecraft have suggested a new energization process in the cusp [Chen et al., 1997; 1998].Simultaneous enhancement of H +, He +2, and 0 >+2 fluxes indicates that they are of solar wind origin.In the present study, we examine H + and He +2 energy spectra from 20 eV to several 100 keV measured by the Hydra, Toroidal Imaging Mass-Angle Spectrograph (TIMAS), and Charge and Mass Magnetospheric Ion Composition Experiment (CAM-MICE) on POLAR.The combined spectrum for each species is shown to be continuous with a thermal distribution below 10 keV/e and an energetic component above 20 keV/e.Energetic ions with comparable fluxes and a similar spectral shape are commonly observed downstream from the Earth's quasi-parallel (Qll) bow shock.In addition to the similarity in the ion spectra, electric and magnetic field noise and turbulence detected in the cusp by the Plasma Wave Instrument (PWI) and Magnetic Field Experiment (MFE) onboard POLAR are similar to the previously reported observations at the bow shock.The waves appear to be coincidental to the cusp energetic ions rather than causal.We suggest that these ions are not accelerated locally in the cusp.Rather, they are accelerated at the QII bow shock and enter the cusp along open magnetic field lines connecting both regions.component, have been long understood to be directly from the solar wind.The energetic particle data from the PO-LAR spacecraft recently called into question the origin of high-energy plasmas in the cusp.These cusp energetic particles (CEPs) first documented in the CAMMICE and CEP-PAD data have energies above the typical solar wind energies up to hundreds of keV/e [Chen et al., 1997; 1998].Ion composition measurements show that they are of solar wind origin.Because energetic particles were not observed in the