HR: 0800h
AN: SH51B-1212    [Abstracts]
TI: Upstream Energetic Ions: Leakage or Fermi Acceleration
AU: * Chang, S
EM: shen.chang@msfc.nasa.gov
AF: Center for Space Plasma and Aeronomic Research, Univ. of Alabama in Huntsville, Huntsville, AL 35899 United States
AU: * Chang, S
EM: shen.chang@msfc.nasa.gov
AF: National Space Science and Technology Center, XD12, 320 Sparkman Dr, Huntsville, AL 35805 United States
AU: Kudela, K
EM: kudela@upjs.sk
AF: Institute of Experimental Physics, Slovak Academy of Science, Watsonova 47, Kosice, 04353 Slovakia (Slovak Republic)
AB: Energetic (> 20 keV) ion data collected by the Interball-1 spacecraft upstream from the Earth's bow shock over a period of five years (1995-2000) are analyzed. Most of the enhanced energetic ion flux events occurred when Interball-1 was magnetically connected to the bow shock. In these connected events which occupy ~ 43% of total upstream events, characteristics of bow shock accelerated ions and magnetospheric energetic ions emerge for different ranges of ion energy. Upstream energetic ion flux is anti-correlated with θ_Bn. This correlation weakens with increasing ion energy but greatly improves with more isotropic ion distribution. For diffusive events, ion flux at energies up to ~100 keV becomes strongly anti-correlated with θ_Bn. Other parameters, such as local time, distance from Interball-1 to the shock, Kp and Dst indices, have little influence on the θ_Bn dependence for lower-energy ions. For ions with energy above 150 keV, ion flux is better correlated with Dst than θ_Bn. These results suggest that Fermi acceleration accounts for most of the observed lower-energy ions and contribution from the magnetospheric leakage becomes important for the higher-energy ions. Both solar wind and magnetosphere contribute to the seed particles for the Fermi process at the quasi-parallel bow shock. For bow shock accelerated ions with energy below ~50 keV, seed particles are mainly drawn from the solar wind but above 50 keV, contribution from the magnetosphere is significant and may exceed solar wind contribution.
DE: 2114 Energetic particles (7514)
DE: 2154 Planetary bow shocks
DE: 7845 Particle acceleration
DE: 7851 Shock waves (4455)
SC: SPA-Solar and Heliospheric Physics [SH]
MN: Fall Meeting 2005