Radial and Latitudinal Variations of the Energetic Particle Response to ICMEs

Abstract

We present energetic particle observations during events in which the interplanetary counterpart of a single coronal mass ejection (ICME) has been observed by spacecraft widely separated in radial distance and latitude. The effects that ICMEs have on energetic particle intensities depend on (1) the ability of ICMEs to drive strong shocks able to accelerate energetic particles, (2) the existence of an intra-ICME energetic particle population, and (3) the capability of the ICMEs to confine (or exclude) energetic particles. These three factors depend upon (1) the energy of the particles, (2) the solar wind medium in which the ICMEs propagate, (3) the mechanisms of energetic particle transport within and around the ICMEs, and (4) the magnetic topology of the ICMEs. As ICMEs expand, ICME-driven shocks weaken and intra-ICME magnetic field intensities decrease. These changes, together with the fortuitous occurrence of solar energetic particle events during the transit time of the ICMEs to large distances are the main causes for the different energetic particle signatures observed during the passage of the same ICME at two distant heliospheric locations.