Particle acceleration at coronal mass ejection–driven interplanetary shocks and the Earth's bow shock

Abstract

Particle acceleration in space plasmas, particularly at collisionless shocks, remains a fundamental yet poorly understood problem in space physics. The most important questions that need to be addressed include (1) where are the particles accelerated, (2) what source material is available for acceleration, (3) what mechanisms are responsible for injecting and accelerating the particles, and (4) how are the particle properties modified during their propagation from the acceleration sites to the observation point? Answering these questions will enable further development of the theoretical framework and models that will facilitate quantitative predictions of key properties of the accelerated particles. In this paper, we review recent observations associated with two distinct but widely studied energetic ion populations: (1) solar energetic particles associated with coronal mass ejection–driven interplanetary shocks and (2) energetic ions observed upstream of the Earth's bow shock. We review the common theoretical concepts and physical processes that are believed to be responsible for accelerating particles at these two types of collisionless shocks, emphasizing the commonalities between these distinct structures and their associated particle populations.