Modelling Explosive Events in the Solar Corona.
Lead Research Organisation:
University of Dundee
Department Name: Mathematics
Abstract
The corona - the outer atmosphere of the Sun - is a dynamic plasma permeated by a magnetic field. The corona is a highly dynamic environment, and energy stored in the magnetic field power a range of explosive phenomena such as jets, flares and coronal mass ejections, as well as explaining the heating of the multi-million degree corona and the acceleration of the solar wind. Powerful explosions in the solar corona lead to major space weather events at Earth, creating the Northern and Southern lights but also having the potential for damaging economic impacts on engineered systems, ranging from satellites and communication systems to power grids and pipelines.
Whilst it is now known that the magnetic field on the Sun's corona has a complex and continually evolving structure, the nature and implications of this complexity remain largely unexplored and poorly understood. Fundamental questions include how much magnetic energy is stored in the coronal plasma, and how this energy may be liberated on a dynamical timescale. This project involves the development and use of a combination of theoretical and/or computational modelling techniques to study the structure and dynamics of energetic processes in the corona. A student undertaking the project will gain skills and expertise in modelling and high-performance computing. The results will enhance our understanding of energetic events in plasmas on a range of scales throughout the universe. The project will make use of collaborations both within the group in Dundee and with external international colleagues.
Whilst it is now known that the magnetic field on the Sun's corona has a complex and continually evolving structure, the nature and implications of this complexity remain largely unexplored and poorly understood. Fundamental questions include how much magnetic energy is stored in the coronal plasma, and how this energy may be liberated on a dynamical timescale. This project involves the development and use of a combination of theoretical and/or computational modelling techniques to study the structure and dynamics of energetic processes in the corona. A student undertaking the project will gain skills and expertise in modelling and high-performance computing. The results will enhance our understanding of energetic events in plasmas on a range of scales throughout the universe. The project will make use of collaborations both within the group in Dundee and with external international colleagues.
Organisations
People |
ORCID iD |
| David Pontin (Primary Supervisor) |
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| ST/N504026/1 | 12/09/2016 | 11/09/2021 | |||
| 1868412 | Studentship | ST/N504026/1 | 12/09/2016 | 11/03/2020 |
| Description | Solar weather events can cause significant damage to satellites and ground-based electrical infrastructure. As such, it is important to understand the mechanisms by which energy in the solar corona is stored and released to better predict when such events will occur. The diffuse nature of the corona means that particle acceleration is difficult to observe directly and must be inferred from observations of the solar photosphere (the Sun's effective "surface") and from satellites in Earth's orbit. Comparing these observations with coronal plasma simulations allows us to constrain the conditions and acceleration mechanisms present in the solar atmosphere. We investigated the acceleration of charged particles in the presence of reconnecting magnetic fields, which is a popular candidate for coronal energy release. To this end I wrote a code to model the trajectories of individual charged particles. Dynamically changing the method of tracing these trajectories subject to the local magnetic and electric field conditions allowed for more efficient and accurate results than relying on a single method. While such work in the past has simulated these particles in simplistic magnetic field geometries where the plasma environment is well known at all locations, we instead injected them in snapshots of simulations of reconnecting magnetic fields recently developed by Peter Wyper, David Pontin and C.R. DeVore, interpolating values between grid points. It was found that oppositely charged particles, protons and electrons, are accelerated in opposite directions in isolated reconnecting field-line structures, leading to significant divergence in the trajectories of these two populations. Furthermore the highest-energy particles were seen to align closely with twisted sections of the magnetic field structures, known as flux ropes. When the field geometry is extended to that of a larger structure thought typical in the corona, this directionality results in protons and electrons impacting the photosphere in broadly separate locations. The shape of these impact patterns are consistent with so-called "flare ribbons" observed on the photosphere during flaring events. Particles accelerated into interplanetary space show a similar divergence, ejected from the corona in distinct beams. As the field structure evolves the degree of divergence for both the photospheric and interplanetary-bound populations change, suggesting that this could be used as a means of indirectly monitoring the evolution of coronal magnetic field structures. In addition, the high-energy particles bound to flux ropes are incident on the photosphere as concentrated bright-points, consistent with observations of X-ray "kernels" within and around flare ribbons. The quantity and position of these bright-points change as the field evolved, indicating that these might also be used as a means of inferring the evolution of real magnetic field structures in the corona. |
| Exploitation Route | The code used to simulate the motion of charged particles does not account for all relevant physical effects. While the positions of the photosphere-incident populations can be determined, how they collide with the material of the photosphere is not considered. This is necessary to produce simulated X-ray emissions with which to compare with observational data. Additionally the simulations assume that the magnetic fields do not change in the time it takes for particles to traverse the simulated region. Prior work has shown that time-dependent fields play an important role in the acceleration of nearby particles, so accounting for time-dependence would be a valuable addition to the code. While the photospheric impact positions are consistent with observations, the proton/electron divergence has not yet been consistently observed. Investigating how this divergence may manifest in observations e.g. different observational signals or a time delay for different sections of the flare ribbons would be needed to further substantiate our assertions. If such a divergence is not supported by observations, it would instead be of interest to consider what effect(s) would nullify the divergence and what consequence it would have on other aspects of coronal physics. Finally while the photospheric impacts have been considered at length, the diverging populations ejected into interplanetary space have not been fully investigated. The current field geometry only accounts for the immediate vicinity around the reconnecting fields and the photosphere. Any consideration of what happens to this divergence in interplanetary space and at Earth's magnetosphere would require either an expansion of the simulated field geometry or the development of an entirely new interplanetary particle transport model. |
| Sectors | Aerospace, Defence and Marine,Environment |