Acceleration of solar wind ions by oblique interplanetary shocks

Abstract

This paper compares observations of proton distributions made by the SWICS ion mass spectrometer on Ulysses at nearby interplanetary shocks with Monte Carlo simulations of particle acceleration at oblique collisionless shocks. The shock parameters are obtained from upstream measurements of the solar wind and magnetic field, and the input particles are drawn from convected Maxwellians, representing solar wind particles. Good agreement between downstream spectral measurements and the simulation predictions are obtained by allowing the parameter lambda/r_g, the ratio of the mean-free scattering length to the ionic gyroradius, to vary in an optimization of the fit to the data. Generally lambda/r_g is found to be less than about 20, which corresponds to the case of strong scattering.