Reconnection-driven waves and oscillations in the flaring solar corona

点击翻译按钮获取中文摘要

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.