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Ann. Geophys., 17, 650-658, 1999
www.ann-geophys.net/17/650/1999/
© European Geosciences Union 1999
Characteristics of > 290 keV magnetosheath ions
I. Karanikola, G. C. Anagnostopoulos, and A. Rigas
Department of Electrical Engineering, Demokritos University of Thrace, Xanthi 67100, Greece
E-mail: anagnosto@xanthi.cc.duth.gr
Abstract. We performed a statistical analysis of
290-500 keV ion data obtained by IMP-8 during the years 1982-1988 within the
earth's magnetosheath and analysed in detail some time periods withdistinct ion
bursts. These studies reveal the following characteristics for magnetosheath
290-500 keV energetic ions: (a) the occurrence frequency and the flux of ions
increase with increasing geomagnetic activity as indicated by the Kp index; the
occurrence frequency was found to be as high as P > 42% for Kp >
2, (b) the occurrence frequency in the dusk magnetosheath was found to be
slightly dependent on the local time and ranged between ~30% and ~46% for all Kp
values; the highest occurrence frequency was detected near the dusk magnetopause
(21 LT), (c) the high energy ion bursts display a dawn-dusk asymmetry in their
maximum fluxes, with higher fluxes appearing in the dusk magnetosheath, and (d)
the observations in the dusk magnetosheath suggest that there exist intensity
gradients of energetic ions from the bow shock toward the magnetopause. The
statistical results are consistent with the concept that leakage of
magnetospheric ions from the dusk magnetopause is a semi-permanent physical
process often providing the magnetosheath with high energy (290-500 keV) ions.
Key words. Magnetospheric physics (magnetosheath;
planetary magnetospheres). Space plasma physics (shock waves).
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