The effect of shock wave properties on the release timings of solar energetic particles

Abstract

Context. Fast and wide coronal mass ejections (CMEs) and CME-driven shock waves are capable of accelerating solar energetic particles (SEPs) and releasing them in very distant locations in the solar corona and near-Sun interplanetary space. SEP events have a variety of characteristics in their release times and particle anisotropies. In some events, specifics of the SEP release times are thought to be difficult to reconcile with the scenario that a propagating shock wave is responsible for the SEP release. Aims. Despite the apparent difficulties posed by the shock scenario, many studies have not considered the properties of the propagating shock waves when making a connection with SEP release. This could probably resolve some of the issues and would help us to delve into and understand more important issues such as the effect of the shock acceleration efficiency on the observed characteristics of the SEP timings and the role of particle transport. This study aims to approach these issues from the shock wave perspective and elucidate some of these aspects. Methods. We constructed a simple 2D geometrical model to describe the propagation and longitudinal extension of a disturbance. We used this model to examine the longitudinal extension of the wave front from the eruption site as a function of time, to calculate the connection times as a function of the longitudinal separation angle, and to determine the shock parameters at any connection point. We examined how the kinematic and geometric properties of the disturbance could affect the timings of the SEP releases at different heliolongitudes.Results. We show that the extension of a wave close to the solar surface may not always indicate when a magnetic connection is established for the first time. The first connection times depend on both the kinematics and geometry of the propagating wave. A shock-related SEP release process can produce a large event-to-event variation in the relationship between the connection and release times and the separation angle to the eruption site. The evolution of the shock geometry and shock strength at the field lines connected to an observer are important parameters for the observed characteristic of the release times.

Acceleration and Release of Solar Energetic Particles Associated with a Coronal Shock on 2021 September 28 Observed by Four Spacecraft

“…We note that the release time of particles estimated at STA may be influenced by the in situ magnetic field direction (see Section 4.3 below). The effects of inhomogeneities in the ambient medium leading to different particle properties are not discussed here (e.g., Kouloumvakos et al 2022Kouloumvakos et al , 2023Wijsen et al 2023).…”

Galactic Cosmic Rays and Solar Energetic Particles in Cis-Lunar Space

“…Simulations show, for instance, that pitch-angle scattering can modify the SEP spectrum during propagation [49], while observations show several spectral features that might point to the underlying acceleration process [50]. Widespread SEP events [51] are either a result of a very broad acceleration source or indicate that SEPs can propagate efficiently across the mean magnetic field. This may be due to either perpendicular diffusion [52], drift effects [53,54], or a combination of these processes.…”

PyThea: An open-source software package to perform 3D reconstruction of coronal mass ejections and shock waves

“…Rouillard et al, 2016;Kouloumvakos et al, 2019Kouloumvakos et al, , 2020bGiacalone et al, 2020;Dresing et al, 2022), the wide distribution of SEPs in the heliosphere (e.g. Rouillard et al, 2012;Lario et al, , 2016Lario et al, , 2017Kouloumvakos et al, 2016;Zhu et al, 2018;Rodríguez-García et al, 2021;Kouloumvakos et al, 2022), and the connection of CMEs and shocks to solar radio emission (e.g. Type II, IV radio bursts; Zucca et al, 2018;Morosan et al, 2020;Kouloumvakos et al, 2021;Jebaraj et al, 2021) and solar gammaray bursts (Kouloumvakos et al, 2020a).…”