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The most stringent test of theoretical models of the first-order Fermimechanism at collisionless astrophysical shocks is a comparison of thetheoretical predictions with observational data on particle populations. Suchcomparisons have yielded good agreement between observations at thequasi-parallel portion of the Earth's bow shock and three theoreticalapproaches, including Monte Carlo kinetic simulations. This paper extends suchmodel testing to the realm of oblique interplanetary shocks: here observationsof proton and alpha particle distributions made by the SWICS ion massspectrometer on Ulysses at nearby interplanetary shocks are compared with testparticle Monte Carlo simulation predictions of accelerated populations. Theplasma parameters used in the simulation are obtained from measurements ofsolar wind particles and the magnetic field upstream of individual shocks. Goodagreement between downstream spectral measurements and the simulationpredictions are obtained for two shocks by allowing the the ratio of themean-free scattering length to the ionic gyroradius, to vary in an optimizationof the fit to the data. Generally small values of this ratio are obtained,corresponding to the case of strong scattering. The acceleration processappears to be roughly independent of the mass or charge of the species.Comment: 26 pages, 6 figures, AASTeX format, to appear in the Astrophysical  Journal, February 20, 199

Acceleration of Solar Wind Ions by Nearby Interplanetary Shocks: Comparison of Monte Carlo Simulations withUlyssesObservations