Observational test of shock drift and fermi acceleration on a seed particle population upstream of the Earth's bow shock

Journal Article · Wed Jun 01 00:00:00 EDT 1988 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/JA093iA06p05541· OSTI ID:5258018

Anagnostopoulos, G C; Sarris, E T ^[1]; Krimigis, S M ^[2]

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1. Demokritos Univ. of Thrace, Xanthi (Greece)
2. Johns Hopkins Univ., Laurel, MD (USA)

Simultaneous observations of energetic protons of solar origin by the IMP 7 and 8 spacecraft in the vicinity of the dawn and dusk bow shock, respectively, are examined to determine the conditions for acceleration of an ambient energetic particle population at the bow shock. The data show that acceleration effects are observed in the intensities of the energetic protons with energies as high as E{approximately}4 MeV only at the quasi-perpendicular region of the bow shock. Furthermore, the ion acceleration is observed for high values of the solar wind velocity and the interplanetary magnetic field (IMF) and for an expanded bow shock. The energy spectra and angular distributions of the intensities of the accelerated ions both upstream and downstream from the bow shock are consistent with the predictions of the shock drift acceleration (SDA) mechanism operating efficiently at the quasi-perpendicular (dusk) side of the bow shock while the IMF is in the nominal direction. At the same time no evidence for any particle acceleration at E{approx gt}50 keV was detected by the spacecraft located at the quasi-parallel (dawn) side of the bow shock, under conditions which favor the Fermi mechanism. These results, together with an observation of a magnetospheric burst during a period of radial IMF suggest the following: (1) acceleration of a seed particle population only occurs at the quasi-perpendicular bow shock through SDA and (2) leakage of magnetospheric ions at E {approx gt} 50 keV rather than in situ acceleration is the principal source of observed upstream ion populations.

• OSTI ID: 5258018
• Journal Information: Journal of Geophysical Research; (United States), Vol. 93:A6; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
EARTH MAGNETOSPHERE
SOLAR WIND
SOLAR PROTONS
ACCELERATION
INTERACTIONS
ENERGY SPECTRA
IMP SATELLITES
INTERPLANETARY MAGNETIC FIELDS
ION DRIFT
SHOCK WAVES
VELOCITY
BARYONS
EARTH ATMOSPHERE
ELEMENTARY PARTICLES
FERMIONS
HADRONS
MAGNETIC FIELDS
NUCLEONS
PROTONS
RADIATIONS
SATELLITES
SOLAR ACTIVITY
SOLAR PARTICLES
SOLAR RADIATION
SPECTRA
STELLAR RADIATION
640104* - Astrophysics & Cosmology- Solar Phenomena
640201 - Atmospheric Physics- Auroral
Ionospheric
& Magetospheric Phenomena