Three dimensional numerical simulations of non-linear MHD instabilities in the solar corona
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The aim of this thesis has been to carry out 3D MHD simulations to investigate nonlinear MHD instabilities and the behaviour of solar coronal loops. The simulations have been carried out on a parallel computer using a new shock-capturing Lagrangian-remap code, LareSd. As part of the PhD this code has been extended to include resistivity allowing the study of the non-linear resistive evolution of the instability. In particular the kink instability in line-tied coronal loops has been studied. This was suggested as a possible explanation of compact loop flares, sudden brightenings of a coronal loop due to a release of energy which does not destroy the loop. For the kink instability to explain such flares it must drive reconnection. This requires high current densities, i.e. current sheets. The results presented in this thesis suggest that the formation of current sheets during the non-linear evolution of the kink instability is more complicated than was previously believed. Indeed, if the loop is allowed to evolve slowly until the instability is triggered than the current appears to saturate at a finite value. This suggests that the kink instability cannot explain a compact loop flare. LareSd has also been used to model space observations from NASA’s SoHO (a joint NASA/ESA satellite) and TRACE satellites. These observations showed a group of rotating sunspots and their overlying system of loops. The simulations will allow further investigations of this behaviour to be carried out.
Thesis, PhD Doctor of Philosophy
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