Cannibals in PARADISE: The effect of merging interplanetary shocks on solar energetic particle events

TL;DR

This paper presents the first fully time-dependent 3D MHD simulation of CME-CME interactions and their impact on solar energetic particle acceleration, revealing enhanced particle energies during shock merging.

Contribution

It introduces a novel integrated MHD and SEP modeling approach to simulate CME interactions and their effects on particle acceleration in the heliosphere.

Findings

Particle acceleration is initially less efficient with separate CMEs.

Shock merging significantly enhances particle acceleration.

Higher particle energies and intensities occur after CME shocks merge.

Abstract

Gradual solar energetic particle (SEP) events are associated with shocks driven by coronal mass ejections (CMEs). The merging of two CMEs (so-called Cannibalistic CMEs) and the interaction of their associated shocks, has been linked to some of the most powerful solar storms ever recorded. Multiple studies have focused on the observational aspects of these SEP events, yet only a handful have focused on modeling similar CME-CME interactions in the heliosphere using advanced magnetohydrodynamic (MHD) models. This work presents, to our knowledge, the first modeling results of a fully time-dependent 3D simulation that captures both the interaction of two CMEs and its effect on the acceleration and transport of SEPs. This is achieved by using an MHD model for the solar wind and CME propagation together with an integrated SEP model. We perform different simulations and compare the behavior of the energetic protons in three different solar wind environments, where a combination of two SEP-accelerating CMEs are modeled. We find that particle acceleration is significantly affected by the presence of both CMEs in the simulation. Initially, less efficient acceleration results in lower energy particles. However, as the CMEs converge and their shocks eventually merge, particle acceleration is significantly enhanced through multiple acceleration processes between CME-driven shocks, resulting in higher particle intensities and energy levels.