Open AccessFermi acceleration of suprathermal solar wind oxygen ions
Author(s) -
Freeman T. J.,
Parks G. K.
Publication year - 2000
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/1999ja900501
Subject(s) - physics , solar wind , fermi acceleration , ion , atomic physics , interplanetary medium , solar energetic particles , computational physics , spectral line , particle acceleration , polar wind , bow shock (aerodynamics) , interplanetary magnetic field , astrophysics , plasma , interplanetary spaceflight , coronal mass ejection , astronomy , shock wave , nuclear physics , mechanics , quantum mechanics
The Wind spacecraft has observed numerous sunward bursts of ≈2 MeV ions upstream of the Earth's bow shock. These energetic particles are not protons or alpha particles and are probably oxygen ions. The bursts typically last several minutes at the highest energies, but they can last for tens of minutes at intermediate energies (tens to hundreds of keV). In this paper, Wind observations of the November 30, 1994, bursts and numerical particle simulations are presented that demonstrate that suprathermal solar wind O 6+ ions, which have undergone Fermi acceleration between the bow shock and interplanetary magnetic field (IMF) rotations, are the most likely source of these bursts. Each burst either coincides with or is closely followed by a large IMF rotation. By using measured magnetic field data the timing of the bursts detected by Wind is reproduced in the simulation. Simulated spectra of H + , He 2+ , and O 6+ fluxes fit the observed spectra, assuming an increase of ∼2 orders of magnitude in the high‐energy tail of the solar wind oxygen distribution, relative to the average solar wind abundance of oxygen. Such enhancements in CNO group ions above 40 keV/nucleon were measured by the Suprathermal and Energetic Particle (STEP) instrument during this interval. This study concludes by predicting that ion composition and charge state measurements will show these bursts to be solar wind oxygen ions in high charge states.