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GEOPHYSICAL RESEARCH LETTERS, VOL. 25, NO. 19, PAGES 3729–3732, 1998

Cusp Energetic Ions: A Bow Shock Source

S. -W. Chang

Department of Physics and Astronomy, University of Iowa, Iowa City.

J. D. Scudder

Department of Physics and Astronomy, University of Iowa, Iowa City.

S. A. Fuselier

Lockheed Martin Advanced Technology Center, Palo Alto, California.

J. F. Fennell

The Aerospace Corporation, Los Angeles, California.

K. J. Trattner

Lockheed Martin Advanced Technology Center, Palo Alto, California.

J. S. Pickett

Department of Physics and Astronomy, University of Iowa, Iowa City.

H. E. Spence

Center for Space Physics, Boston University, Boston, Massachusetts.

J. D. Menietti

Department of Physics and Astronomy, University of Iowa, Iowa City.

W. K. Peterson

Lockheed Martin Advanced Technology Center, Palo Alto, California.

R. P. Lepping

NASA Goddard Space Flight Center, Greenbelt, Maryland.

R. Friedel

Los Alamos National Laboratory, Los Alamos, New Mexico.

Abstract

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 O^>+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 (CAMMICE) 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 (Q_∥) 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 Q_∥ bow shock and enter the cusp along open magnetic field lines connecting both regions.

Received 18 June 1998; accepted 25 August 1998.

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Citation: Chang, S. .-W., et al. (1998), Cusp Energetic Ions: A Bow Shock Source, Geophys. Res. Lett., 25(19), 3729–3732.

Copyright 1998 by the American Geophysical Union.