Physics
Scientific paper
Feb 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994jgr....99.2335a&link_type=abstract
Journal of Geophysical Research (ISSN 0148-0227), vol. 99, no. A2, p. 2335-2349
Physics
17
Alpha Particles, Magnetosheath, Plasma Acceleration, Plasma Drift, Protons, Shock Waves, Bow Waves, Electron Energy, Energy Spectra, Magnetohydrodynamic Flow, Plasma Density, Solar Wind
Scientific paper
We present simultaneous energetic proton (E greater than or equal to 50 keV), alpha particle (E greater than or equal to 37 keV/n) and electron (E greater than or equal to 220 keV) observations obtained by the spacecraft IMP 8 and IMP 7 for an extended time period on May 2 and 3, 1976. During that time period, IMP 8 crossed successively the quasi-perpendicular duskside of the bow shock in the presence of high fluxes of the ambient solar energetic particle population and under solar wind conditions which implied in a large value of the induced electric field E and a small ratio r(sub G)/R(sub c) of the initial proton gyroradius to the local radius of curvature. The observations indicate that three different types of energetic ion populations can be distinguished inside the magnetosheath for the time period examined: (1) energetic ions of solar origin accelerated at (quasi-)perpendicular regions of the bow shock via the shock drift acceleration (SDA) process, (2) energetic ions of solar origin not affected by the bow shock, and (3) energetic ions of magnetospheric origin. Protons and alpha particles accelerated and transmitted downstream from the bow shock conserve the same spectral index of the ambient solar population at low energies (50 less than or equal to E less than or equal to 360 keV) and present small values of the peak-to-background intensity ratio p/b ranging between 2.1 and 3.8 in the cases examined. A characteristic signature of the SDA, the double-peaked anisotropy of the angular distributions of the particle intensities is not always observable in the low-energy range (50 less than or equal to E less than or equal to 290 keV), because of the influence of the plasma flow in the magnetosheath, but is always observed in the high-energy range (E is greater than or equal to 290 keV). Acceleration effects in the vicinity of the (quasi-)perpendicular (Theta(sub Bn) is approximately equal to 79 deg - 90 deg) bow shock are observed in the intensities of the energetic protons with energies as high as E approximately equal to 4 MeV. Protons of magnetospheric origin present values of the ratio p/b as high as approximately 6 x 10(exp 2) and softer energy spectra (gamma is greater than or equal to 4) than those of the protons accelerated at the bow shock.
Anagnostopoulos G. C.
Kaliabetsos G. D.
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