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Annales Geophysicae An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 1
Ann. Geophys., 18, 42–46, 2000
© European Geosciences Union 2000
Ann. Geophys., 18, 42–46, 2000
© European Geosciences Union 2000

  31 Jan 2000

31 Jan 2000

Spatial distribution of upstream magnetospheric ≥50 keV ions

G. C. Anagnostopoulos, G. Argyropoulos, and G. Kaliabetsos G. C. Anagnostopoulos et al.
  • Department of Electrical and Computer Engineering, University of Thrace, Xanthi 67100, Greece
  • E-mail:

Abstract. We present for the first time a statistical study of \geq50 keV ion events of a magnetospheric origin upstream from Earth's bow shock. The statistical analysis of the 50-220 keV ion events observed by the IMP-8 spacecraft shows: (1) a dawn-dusk asymmetry in ion distributions, with most events and lower intensities upstream from the quasi-parallel pre-dawn side (4 LT-6 LT) of the bow shock, (2) highest ion fluxes upstream from the nose/dusk side of the bow shock under an almost radial interplanetary magnetic field (IMF) configuration, and (3) a positive correlation of the ion intensities with the solar wind speed and the index of geomagnetic index Kp, with an average solar wind speed as high as 620 km s-1 and values of the index Kp > 2. The statistical results are consistent with (1) preferential leakage of ~50 keV magnetospheric ions from the dusk magnetopause, (2) nearly scatter free motion of ~50 keV ions within the magnetosheath, and (3) final escape of magnetospheric ions from the quasi-parallel dawn side of the bow shock. An additional statistical analysis of higher energy (290-500 keV) upstream ion events also shows a dawn-dusk asymmetry in the occurrence frequency of these events, with the occurrence frequency ranging between ~16%-~34% in the upstream region.

Key words. Interplanetary physics (energetic particles; planetary bow shocks)

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