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Plasma heating and particle acceleration by magnetic reconnection in solar and stellar flares

Detail Summary
Date 19 June 2019
Time 11:00 - 12:00
Philippa Browning
Philippa Browning (Jodrell Bank Centre for Astrophysics)

Solar flares are dramatic releases of stored magnetic energy in the solar corona, with signatures across the electromagnetic spectrum due to plasma heating and the generation of high-energy electrons and ions. Flares are an underlying cause of space weather events, which can significantly affect satellites as well as power systems and communications on Earth. It is widely accepted that flares result from energy release through magnetic reconnection, but many questions remain.

I will outline recent development in modelling plasma heating and non-thermal particle acceleration in flares, focussing on twisted magnetic flux ropes as reservoirs of free magnetic energy, utilising magnetohydrodynamic simulations coupled to a test-particle code.  Considering first a large-scale flaring current sheet driven by an external disturbance, I will show how reconnection releases magnetic energy both through creation of twisted flux ropes and their merger. Moving to 3D models, I will show that fragmented current structures in kink-unstable flux ropes provides effective   plasma heating and non-thermal particle acceleration.  Forward modelling of the observational signatures of this process in EUV, hard X-rays and microwaves potentially allows observational identification of twisted magnetic fields in the solar corona. Then, coronal structure with multiple twisted threads will be considered, showing how instability in a single unstable twisted thread may trigger reconnection with stable neighbours, releasing their stored energy and causing an "avalanche" of heating events, with important implications for solar coronal heating by nanoflares. 

Many other stars exhibit flares, and I will also  describe recent work on modelling radio emission in flares in T Tauri stars. In particular, the enhanced radio luminosity of these stars relative to scaling laws for the Sun and other Main Sequence stars will be discussed.