Successive Coronal Mass Ejections Associated with Weak Solar Energetic Particle Events

TL;DR

This study investigates how twin coronal mass ejections influence solar energetic particle events, emphasizing the importance of CME speed, magnetic connectivity, and CME propagation direction in SEP intensity, especially in events without significant SEP detection at L1.

Contribution

It provides a detailed analysis of 19 twin-CME events, highlighting the dominant role of priCME speed and magnetic connectivity in SEP production, and discusses the barrier effect of preCMEs.

Findings

PriCME speed correlates strongly with SEP peak intensity.

Combining CME speed with propagation direction yields higher correlation with SEP intensity.

Magnetic connectivity and lower priCME speed explain SEP-poor twin-CME events.

Abstract

The scenario of twin coronal mass ejections (CMEs), i.e., a fast and wide primary CME (priCME) preceded by previous CMEs (preCMEs), has been found to be favorable to a more efficient particle acceleration in large solar energetic particle (SEP) events. Here, we study 19 events during 2007--2014 associated with twin-CME eruptions but without large SEP observations at L1 point. We combine remote-sensing and in situ observations from multiple spacecraft to investigate the role of magnetic connectivity in SEP detection and the CME information in 3-dimensional (3D) space. We study one-on-one correlations of the priCME 3D speed, flare intensity, suprathermal backgrounds, and height of CME-CME interaction with the SEP intensity. Among these, the priCME speed is found to correlate with the SEP peak intensity at the highest level. We use the projection correlation method to analyze the correlations between combinations of these multiple independent factors and the SEP peak intensity. We find that the only combination of two or more parameters that has higher correlation with the SEP peak intensity than the CME speed is the CME speed combined with the propagation direction. This further supports the dominant role of the priCME in controlling the SEP enhancements, and emphasizes the consideration of the latitudinal effect. Overall, the magnetic connectivity in longitude as well as latitude and the relatively lower priCME speed may explain the existence of the twin-CME SEP-poor events. The role of the barrier effect of preCME(s) is discussed for an event on 2013 October 28.