Sources of solar energetic particles

Abstract

Solar Energetic Particles (SEP) are an integral part of the physical processes related with Space Weather. We present a review for the acceleration mechanisms related to the explosive phenomena (flares and/or CMEs) inside the solar corona. For more than 40 years, the main 2D cartoon representing our understanding of the explosive phenomena inside the solar corona remained almost unchanged. The acceleration mechanisms related to solar flares and CMEs also remained unchanged and were part of the same cartoon. In this review, we revise the standard cartoon and present evidence from recent global MHD simulations that supports the argument that explosive phenomena will lead to the spontaneous formation of current sheets in different parts of the erupting magnetic structure. The evolution of the large scale current sheets and their fragmentation will lead to strong turbulence and turbulent reconnection during solar flares and turbulent shocks. In other words, the acceleration mechanism in flares and CME-driven shocks may be the same, and their difference will be the overall magnetic topology, the ambient plasma parameters, and the duration of the unstable driver.

CME Magnetic Structure and IMF Preconditioning Affecting SEP Transport

“…Contrarily to flares that accelerate particles only on the solar surface, CME-driven shocks may accelerate particles locally in the low corona and also at large distances in the heliosphere, with acceleration sites that typically extend much wider. These two forms of SEP production have traditionally resulted in a clear distinction of particle acceleration processes (e.g., Cane, McGuire, & von Rosenvinge, 1986;Reames, 2013;Vlahos, Anastasiadis, Papaioannou, Kouloumvakos, & Isliker, 2019) into flare-accelerated (often with an impulsive profile; e.g., Reames, 1990) and shock-accelerated (more likely to show a gradual time evolution; e.g., Desai & Giacalone, 2016). This 'dual nature' of SEPs, however, is not fully representative of the complex nature and interplay of processes that result in particle injection and acceleration, given that different mechanisms can contribute to a single event (e.g., Anastasiadis, Lario, Papaioannou, Kouloumvakos, & Vourlidas, 2019;Cane, Richardson, & von Rosenvinge, 2010).…”

The Solar Origin of Particle Events Measured by Parker Solar Probe

“…Two decades of continuous measurements of solar energetic particles (SEPs) and simultaneous remote-sensing observations of the solar corona have significantly improved our understanding of the origin of energetic particles and their distribution in the heliosphere. Two dominant acceleration sites are involved in the generation of SEP events (see reviews by Desai & Giacalone 2016;Reames 2017;Vlahos et al 2019, and references therein). One occurs in solar flares and the other in shocks driven by coronal mass ejections (CMEs) in the corona and interplanetary medium.…”

Developing a Nowcasting Capability for X‐Class Solar Flares Using VLF Radiowave Propagation Changes.

“…The X‐rays produced from a solar flare on the Earth‐facing side of the Sun directly impacts the dayside ionosphere. Following the solar flare occurrence, there can be two additional potential sources of disturbance to Earth‐based technological systems: solar proton events (Ryan et al, ; Vlahos et al, ) with their potential to cause polar cap absorption of HF communications, and coronal mass ejections (Lilensten & Bornarel, ). There is not a straightforward relationship between the intensity of a solar flare and the severity of the solar proton events and coronal mass ejection effects that follow.…”