Observational test of shock drift and Fermi acceleration on a seed particle population upstream of earth's bow shock

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 duringmore » 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.« less

[1]  S. Krimigis,et al.  Upstream energetic ions under radial IMF: A critical test of the Fermi Model , 1988 .

[2]  S. Krimigis,et al.  Further on the October 31, 1977 upstream event: A response to D. C. Ellison , 1987 .

[3]  S. Krimigis,et al.  Simultaneous measurements of energetic ion (≥50 keV) and electron (≥220 keV) activity upstream of Earth's bow shock and inside the plasma sheet: Magnetospheric source for the November 3 and December 3, 1977 upstream events , 1987 .

[4]  F. Boudier,et al.  Structure of Zabargad Island and early rifting of the Red Sea , 1987 .

[5]  David G. Sibeck,et al.  Magnetospheric particle injection and the upstream ion event of September 5, 1984 , 1986 .

[6]  S. Krimigis,et al.  Magnetospheric origin of energetic (E ≥ 50 keV) ions upstream of the bow shock: The October 31, 1977, event , 1986 .

[7]  F. Ipavich,et al.  Energetic ions upstream of the Earth's bow shock during an energetic storm particle event , 1983 .

[8]  E. Sarris,et al.  Dominant acceleration processes of ambient energetic protons (E ⩾ 50 keV) at the Bow Shock: Conditions and limitations , 1983 .

[9]  Martin A. Lee.  Coupled hydromagnetic wave excitation and ion acceleration upstream of the earth's bow shock , 1982 .

[10]  A. Galvin,et al.  A Statistical survey of Ions Observed Upstream of the Earth's Bow Shock' , 1981 .

[11]  G. Gloeckler,et al.  Conditions for acceleration of energetic ions ≳30 keV associated with the Earth's bow shock , 1980 .

[12]  S. Krimigis,et al.  Simultaneous multispacecraft observations of energetic proton bursts inside and outside the magnetosphere , 1978 .

[13]  S. Krimigis,et al.  Observations of magnetospheric bursts of high-energy protons and electrons at ∼35 RE with Imp 7 , 1976 .

[14]  S. Krimigis.  Energetic ions upstream of planetary bow shocks - Fermi acceleration or leakage? , 1986 .

[15]  Martin A. Lee,et al.  A simple model for the formation of “reflected,” “intermediate,” and “diffuse” ion distributions upstream of Earth's bow shock , 1985 .

[16]  S. Krimigis,et al.  ENERGETIC PARTICLE BURSTS IN THE EARTH'S MAGNETOTAIL , 1979 .

[17]  S. Krimigis,et al.  Acceleration and modulation of electrons and ions by propagating interplanetary shocks , 1977 .