The Influence of the Upstream Medium Conditions on the Properties of the Energetic Particle Intensity Enhancements Associated with Interplanetary Shocks

The properties of the distributions of suprathermal particles accelerated at collisionless shocks in the interplanetary medium depend not only on the shock parameters but also on the transport conditions experienced by the particles as they propagate away from the shocks. The confinement of particles in close proximity to the shocks by scattering processes undergone by the particles or by intervening interplanetary structures, may result in local proton intensity enhancements that, at 1 au, occasionally may reach high ($\sim$100 MeV) energies. On the other hand, a shock propagating through an upstream medium characterized by a smooth magnetic field devoid of significant magnetic field fluctuations, may show prolonged anisotropic, field-aligned particle beams before shock passage. We will show examples of both cases and discuss how the properties of the upstream medium and the capability of the shock-accelerated particles to drive field instabilities may shape the properties of the energetic particle enhancements observed at the passage of transient interplanetary shocks.