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Transverse waves in simulated coronal loops: their potential in coronal heating and seismology

Book - Dissertation

Waves have been found to be ubiquitous in the solar atmosphere. They could carry a large amount of energy and may play an important role in coronal heating. The study on waves provides us not only a way to approach the coronal heating problem, but also a tool to diagnose physical parameters that are not easy to measure in reality. This project will focus on the potential of oscillations both in heating the solar corona and in indirectly inferring the atmospheric parameters, under the framework of magnetohydrodynamics (MHD).We considered the oscillations in a magnetic cylinder with different footpoint drivers, namely a kink driver, an Alfven driver, and a mix of the two, and found that the loop with a mixed footpoint driver is more efficient in wave energy dissipation. Our forward models indicate that neither Alfven oscillations or the generated fine structures can be adequately resolved given the spatial resolution of available instruments. This means that although difficult to measure at this stage, Alfven oscillations resulting from footpoint swirling motions are likely to be present in coronal loops. And when Alfven oscillations do exist together with kink oscillations, enhanced heating is expected when compared with the cases where only an individual type of drivers is present. Then, we went a further step to find out that the multistranded coronal loop is more efficient in starting the dissipation process. In addition, the temperature profile in the multistranded loop agrees with the previous predictions and observations. Thus the multistrandedness of loops should also be considered in wave-based heating mechanism studies, given our results and the observational facts that the coronal loops should be multistranded.We also examined transverse oscillations in magnetic cylinders with elliptical cross-sections, motivated by recent observations. Given the lack of rotational symmetry of the considered equilibria, we distinguish between two independent polarizations, one in the direction of the major axis and the other along the minor one. Both types of modes undergo a Gaussian damping profile and then an exponential profile, for loops with both circular cross-sections and elliptical cross-sections. Based on such a property, a new seismology scheme can be proposed to infer the parameters in typical active region loops.
Publication year:2020