Particle Acceleration and Alfv’en Wave Generation at the April 4, 2001 Interplanetary Shock

Based on the theory of diffusive shock acceleration of charged particles, we investigate the formation of proton spectra and the generation of an Alfv’en turbulence spectrum by accelerated (storm) particles at the interplanetary shock front in the event occurred at 14:22 UT on April 4, 2001. We formulate a scenario whereby a satisfactory theoretical description of the observed proton and Alfv’en wave spectra obtained from measurements becomes possible: the propagation of solar cosmic rays in interplanetary space before the interplanetary shock arrival at the Earth’s orbit creates an enhanced level of Alfv’en turbulence in the solar wind, which reduces the diffusion coefficient of particles and increases the efficiency of their acceleration.