Impact of magnetic complexity in solar and astrophysical plasmas: Dundee-Durham consortium

This project is a continuation of a successful collaboration between the researchers of the Universities of Dundee and Durham on the behaviour of complex magnetic fields in astrophysical plasmas. Magnetic fields are ubiquitous in astrophysics. Closest to home they are generated inside rotating stars and planets (like the Sun and Earth), but they permeate much of the intervening space - for example, the Earth sits within the magnetised solar wind. Further afield, magnetic fields are observed on scales as vast as that of whole galaxies and as small as that of neutron stars. Where we observe them closely with modern telescopes, such as in the Sun's atmosphere, we find that these magnetic fields are highly complex, having spatial structure down to the smallest observable scales and significant dynamical behaviour. Magnetic fields play a crucial role in determining the behaviour of many of these systems - however, the implications of their ubiquitous complexity remain largely unexplored and poorly understood.

The most spectacular impacts of magnetic fields are often found in the tenuous plasma above the visible surface of stars. In the Sun's atmosphere, for example, the magnetic field is responsible for creating long-lived structures such as coronal loops, for heating the corona to its multi-million degree temperatures, and for explosive events such as solar flares and coronal mass ejections. These powerful explosions 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. Yet these solar magnetic explosions are pitifully weak by comparison with the huge bursts observed from distant magnetars; perhaps not surprising given that these have the strongest magnetic fields known in the Universe.

The overarching aim of the consortium is to explore the causes of magnetic complexity, and to determine its possible large-scale consequences. Can we explain the latest generation of high-resolution observations? Can this small-scale complexity have a significant effect even when we cannot observe it directly? How does the dynamical behaviour of magnetic fields lead to solar eruptions or magnetar bursts?

The various projects within the consortium will carry out theoretical and numerical modelling for a range of different setups, carefully chosen to model the essential features of astrophysical plasmas including coronal loops, solar flares, neutron stars, and the sources of coronal mass ejections and the solar wind. Importantly, the modelling will take input from the latest generation of telescopes - several of our solar models will be directly "data-driven", and observations will be used to validate output. Many of our model predictions will be tailored to upcoming new observations, including those from DKIST and Parker Solar Probe. As well as probing the fundamental physics of astrophysical plasmas, the insight gained from our simulations will have practical application in the space-weather forecasting community. It is becoming apparent that forecasting the occurrence and impact of space weather events cannot rely on static extrapolation models but requires a deep understanding of the dynamical behaviour, and potentially the fine structure, of the Sun's magnetic field.

Eruptive magnetic storms on the Sun (Coronal Mass Ejections) regularly reach the Earth's space environment. The economic consequences of this space weather can be severe, and include damage to satellites and power grids, corrosion of oil and gas pipelines and disruption of communication systems. Furthermore, these events may endanger the health of astronauts and those onboard high-flying aircraft. The proposed research seeks to develop an understanding of how complex magnetic structures in the Sun's atmosphere change and interact, with these interactions being a critical part of the chain of events that generates solar eruptions. As such, a possible major impact of the proposed research will be on the international effort to develop reliable space-weather forecasting systems. (Given notice, defensive measures can be taken against the aforementioned effects.) Projects 1.1, 1.2, and 1.4 address the formation of the slow solar wind, properties of solar flare ribbons, and triggering of coronal mass ejections, and will all help to improve our knowledge of the space weather in proximity of the Earth. In addition, Project 1.5, examining the dynamics of the global solar corona, will allow for significantly improved simulations of the Sun's magnetic field on global scales. This will have potential impacts on short and longer-term forecasting both of the ambient solar wind and of coronal mass ejections. Impacts will be enabled by a direct feeding of project results into space weather prediction efforts at both NASA Goddard Space Flight Center and the UK Met Office, through direct collaborations of the project investigators.

By improving modelling techniques for the heliospheric magnetic field, Project 1.5 could also impact on reconstructions of the Sun's magnetic field in the past. This will affect studies of the long-term variation of solar activity, and, in turn, reconstructions of the Earth's climate in the past.

All projects investigate the dynamics and structure of complex magnetic fields, a fundamental problem of astrophysical and laboratory plasmas (e.g., in controlled thermonuclear fusion). These projects should also be seen in the wider framework of the analysis of complex multi-scale systems which we encounter in many areas of science: the weather, cellular networks, material sciences, neurosciences, nuclear sciences, etc. The theoretical tools and methods created for investigating astrophysical plasmas have both benefited from and contributed to progress in these areas, via exchanges of ideas, software and human resources.

More generally, astronomy has a strong cultural impact. Due to the Sun's close proximity and the stunning images being gathered by new satellites, solar physics has a great capacity to get young people interested in science, as do the extreme conditions and exotic physics in neutron stars (project 2.1). Inspiring new scientists is essential for contributing to UK's skilled labour market. We will engage with schools and the general public on our research findings through schools outreach, public lectures, press releases, online articles or science 'nuggets', and public events such as the Dundee Science Festival. These methods are further documented in the Outreach section of the Impact Plan document.

Members of the consortium have continued to attract funding (including from the Carnegie Trust, the RAS, LMS, IAESTE and BP) to support summer research bursaries for talented undergraduate students both in Dundee and Durham. This has provided graduates with high-level skills in modelling, programming and high-performance computing, highly sought after across a broad range of employment sectors.