The emergence of magnetic flux and its role on the onset of solar dynamic events

Abstract

A plethora of solar dynamic events, such as the formation of active regions, the emission of jets and the occurrence of eruptions is often associated with the emergence of magnetic flux from the interior of the Sun to the surface and above. Here, we present a short review on the onset, driving and/or triggering of such events by magnetic flux emergence. We briefly describe some key observational examples, theoretical aspects and numerical simulations, towards revealing the mechanisms that govern solar dynamics and activity related to flux emergence. We show that the combination of important physical processes like shearing and reconnection of magnetic fieldlines in emerging flux regions or at their vicinity can power some of the most dynamic phenomena in the Sun on various temporal and spatial scales. Based on previous and recent observational and numerical studies, we highlight that, in most cases, none of these processes alone can drive and also trigger explosive phenomena releasing considerable amount of energy towards the outer solar atmosphere and space, such as flares, jets and large-scale eruptions (e.g. coronal mass ejections). In addition, one has to take into account the physical properties of the emerging field (e.g. strength, amount of flux, relative orientation to neighbouring and pre-existing magnetic fields, etc.) in order to better understand the exact role of magnetic flux emergence on the onset of solar dynamic events. This article is part of the theme issue ‘Solar eruptions and their space weather impact’.

Sources of solar energetic particles

“…Solar ARs, coronal holes and the quiet sun are all driven by the turbulent photospheric flows and the emergence of new magnetic flux (see Archontis and Syntelis [13] in the current issue). The acceleration mechanisms for SEP are closely related with the evolution of the 3D eruptive magnetic topologies and the energy release processes [45].…”

“…In this review, we stress two important points: (a) How the photospheric turbulence drives the spontaneous formation of current sheets during solar eruptions (see the brief discussion in §3, where we emphasize the data-driven MHD modelling, and see more details in the article by Archontis & Syntelis [13]), and (b) how the unstable large-scale magnetic topologies sustain strong turbulence, which is crucial for particle acceleration in solar flares and CME-driven shocks. We believe that current data-driven large-scale 3D MHD simulations are closer to a realistic scenario for the acceleration of the SEP [14].…”

Impact of small-scale emerging flux from the photosphere to the corona: a case study from IRIS

“…A decade of observations of small-scale emerging flux regions (EFRs) in the solar atmosphere, carried out with increasing spatial resolution, has reinforced the idea that magnetic reconnection is likely to occur when the newly emerging magnetic flux interacts with the pre-existing ambient fields (e.g., Guglielmino et al 2010, Ortiz et al 2014, Toriumi et al 2017. This process results in energy release, which is able to heat the upper atmospheric layers and to drive high-temperature plasma flows, according to early models (Shibata et al 1989, Yokoyama & Shibata 1995 and more recent numerical simulations (e.g., MacTaggart et al 2015, Archontis & Syntelis 2019, Isliker et al 2019.…”

Introduction to the physics of solar eruptions and their space weather impact

“…One of the key physical processes making solar magnetic activity possible is the emergence of magnetic flux from the interior of the Sun towards the surface and the outer solar atmosphere. The first review [4] discusses the mechanisms of solar eruptions originating from emerging flux regions. Observational examples of eruptive events and numerical simulations of magnetic flux emergence present some of the most recent developments and advances related to multi-scale eruptions and ejections of hot and cool magnetized plasma (e.g.…”

“…The progress needed to improve both the short and the long-term forecasting is enormous and it challenges our entire understanding of the problem [2]. In this issue, we address four interrelated topics, namely: (i) the driving and triggering mechanisms of solar eruptions [3,4], (ii) the prediction of the geoeffective properties of CMEs [2], (iii) the Solar Energetic Particles (SEPs) [5,6] and (iv) the interaction of CMEs with Earth's magnetic field [7][8][9].…”