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Title: Compressive magnetohydrodynamic waves in the solar atmosphere
Author: Yuan, Ding
ISNI:       0000 0004 2749 387X
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2013
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For last decades, magnetohydrodynamic (MHD) waves arise to a hot topic of solar physics. With modern instruments, MHD wave modes are reliably detected, not only for their potential to heat the solar corona, but also as a new tool to diagnose the plasma parameters remotely (MHD seismology). In this thesis, we use space-borne EUV/UV imagers and ground-based observatories to study compressive MHD waves in coronal loops and sunspots. We identify several instrumental artifacts and formulate the scheme to estimate the imager data noise. The diagnostic potential of MHD waves in various plasma structures are also investigated. The orbit-related long periodicities (30-96 min) in the TRACE images and the derotation-induced short periodicy (3-9 min) in the SDO/AIA images are studied and quantified. The methods are proposed to mitigate the effects of such artificial periodicities. The noise level of AIA images is formulated. In sunspots, the 5–min oscillation power usually forms a ring structure enclosing the sunspot umbra. The phase variation was found to display high-order MHD azimuthal body modes. The mode numbers were measured and justified by significance tests. A multi-level observation of magnetoacoustic waves in sunspot was performed. The variation of the magnetoacoustic cut-off frequency over sunspot cross-sectional geometry and sunspot atmosphere was quantified and exploited to diagnose the inclination angle of the magnetic field. To automatically measure the propagating speed of compressive MHD waves, we designed cross-fitting technique (CFT), 2D coupled fitting (DCF) and best similarity measure (BSM). Parametric studies were performed to confirm the validity and robustness of these methods. Distinct propagating fast wave trains were found to be associated with radio bursts that were generated by the flare-accelerated non-thermal electrons. The stretching wavelength along the waveguide implies that the wave trains were impulsively triggered. The wave parameters are measured to probe the properties of guided fast waves. The connectivity between different levels of sunspots and the associated active regions were studied. The long period oscillations were found in both the chromosphere and the corona. The periodicity was close to typical solar interior g-modes.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QB Astronomy ; QC Physics