DOMINANT ACCELERATION PROCESSES OF ENERGETIC PROTONS AT THE EARTHS BOW SHOCK

We examined magnetic field and energetic (E greater than or equal to 30 keV) proton and (E greater than or equal to 220 keV) electron observations obtained by the spacecraft IMP-6, 7, and 8 in the vicinity of both the (quasi-) parallel and (quasi-) perpendicular bow shock of the Earth. The observations analysed show that: (a) for a quasi-perpendicular (45 less than or equal to theta(Bn) < 90 degrees) region of the bow shock, the downstream proton fluxes are higher (lower) than the upstream fluxes, at low (high) energies, (b) for an oblique (30 less than or equal to theta(Bn) < 70 degrees) bow shock there exists a strong positive correlation of the (less than or equal to 30 keV) beam events published by Paschmann et al. [15] with the ambient solar similar to 50 keV proton flux, and similar positive correlation with the value of the induced electric field E = -U-SW x B (c) for parallel or quasi-parallel shocks and strong upstream magnetic wave activity, the presence of upstream > 50 keV ion events is not a continuous phenomenon, but is strongly correlated with the substorm activity of the magnetosphere. The above observations along with other previously published observations are discussed in the context of the Shock Drift Acceleration (SDA) and the Diffusive (1st order Fermi) acceleration theories. We infer that: (a) a seed population of superthermal (energetic) protons are accelerated to higher energies at the oblique (quasi-perpendicular) bow shock via the SDA process, and (b) there is no convincing evidence for acceleration of either the solar wind or ambient energetic ions to energies greater than or equal to 30-50 keV via the Fermi acceleration process.