Reconnection-driven waves and oscillations in the flaring solar corona

Solar flares are the most powerful explosions in the solar system, resulting in extremely hot plasma (tens of millions of degrees Kelvin) and beams of highly-energetic charged particles. Flares can affect the Earth and our space environment in many ways, through "space weather". Furthermore, the existence of a hot corona is likely to result from the combined effect of many small flare-like events known as nanoflares. Whilst it is widely accepted that flares are caused by a release of stored magnetic energy through the process of "magnetic reconnection", involving rapid restructuring of the magnetic field, there are many unanswered questions about how energy is released and charged particles are accelerated.
It is known that the solar corona is highly dynamic and is full of magnetic waves. Whilst much attention has been devoted to understanding how waves may propagate from the interior of the Sun to the corona, and to how these waves propagate and dissipate in the highly-structured coronal magnetic field, much less is known about how waves may be generated in the corona itself by magnetic reconnection. We address this question here, bringing together the study of waves and magnetic reconnection which are usually treated separately.
Twisted bundles of magnetic field lines known as flux ropes are reservoirs of free magnetic energy, and are thus likely sites for solar flares. Previous theoretical studies, confirmed by observations, have shown that the kink instability of twisted flux rope may trigger a release of stored magnetic energy, heating the plasma and accelerating electrons and ions. Furthermore, merging of two or more flux ropes into a single flux rope also releases magnetic energy. Simulations of these processes show that waves and oscillations are usually present, but the properties of these waves and oscillations have not been investigated. We will conduct advanced numerical simulations of energy release in twisted magnetic flux ropes in configurations relevant to solar flares (merger of two flux ropes, creation and merger of flux ropes within a large-scale current sheet, kink instability of a single flux rope, avalanches of heating triggered by one unstable twisted thread), coupling magnetohydrodynamics to model the large-scale magnetic evolution and test-particles and kinetic models to follow the non-thermal energetic particles. We will explore the waves and oscillations which are generated, and how these depend on the magnetic configuration and the external driving. By forward modelling, we will predict observable signatures in thermal and non-thermal emission, particularly microwave/radio emission arising fromn gyration of the energetic electrons in the magnetic fields. These results will be used to interpret existing observations, and to guide future observations, for example with Parker Solar Probe and the Square Kilometre Array.

The public engagement work of Jodrell Bank formed a top-ranked case study for research impact in REF2014 and helped the School of Physics and Astronomy achieve the top grade for impact of any physics department in the UK. The Discovery Centre has a strong track record in engaging with "hard to reach" audiences, including high profile activities such as Stargazing Live and the Bluedot Festival. PKB is strongly engaged with this activity: she regularly contributes to "Meet the Expert" (question and answer sessions involving members of the public ranging from small children to the elderly) and widening-participation schools' days, and has given public lectures to large audiences at the Bluedot festival. PKB also regularly lectures to astronomy societies, science festivals, SciBars, schools and colleges. She has explained her research on nanoflares on the BBC "Sky at Night", as well as appearing on CBBC Newsround, and BBC Breakfast TV, and being a discussant on Radio 4 "In Our Time". JBCA research students run a twice-monthly podcast, the Jodcast, which celebrated its 10th anniversary in Jan 2016; PKB has contributed several times to this, and STFC-funded PhD students in solar physics play a leading role in running the Jodcast.
The proposed research - as well as having direct academic impact within solar physics - will have significant benefits for space weather and fusion. Space weather has potentially large societal and economic effects, and energetic particles play a crucial role in space weather. The improved understanding of particle acceleration and magnetic reconnection will also be of interest in many astrophysical applications. The Sun is a natural plasma physics laboratory, and PKB plays a leading role in encouraging interactions between the solar and fusion plasma communities. For example, she was until recently Chair of the IOP Plasma Physics Group, which brings together all aspects of plasma physics, and is on the EPSRC Fusion Advisory Board. She is a co-investigator in a project funded by Eurofusion led by CCFE to model filaments in the edge region of spherical tokamaks. The latter is an excellent example of the potential "impact" of solar research on fusion plasmas, as the idea is to exploit the understanding of 3D reconnection developed in solar physics in order to model 3D reconnection in filaments emerging though the edge magnetised-plasma.
Previous PDRAs and PhD students supervised by PKB have gone on to successful careers in academia and beyond (e.g Head of Science, AWE; Director of Research, J P Morgan; physics teacher; research fellow at Los Alamos; professors and readers at Princeton, UClan and Sheffield). The valuable training provided in problem solving, mathematical modelling and computer simulation is an important spinoff benefit of our research activity.
The research also has impact for undergraduate and postgraduate teaching, generating MPhys and MSc projects which train students in solar physics and plasma physics as well as more transferable skills such as numerical methods and computer programming.