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Compressive magnetohydrodynamic waves in the solar atmosphere
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Yuan, Ding (Researcher in physics) (2013) Compressive magnetohydrodynamic waves in the solar atmosphere. PhD thesis, University of Warwick.
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WRAP_THESIS_Yuan_2013.pdf - Submitted Version Download (6Mb) | Preview |
Official URL: http://webcat.warwick.ac.uk/record=b2689009~S1
Abstract
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.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QB Astronomy Q Science > QC Physics |
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Library of Congress Subject Headings (LCSH): | Magnetohydrodynamic waves, Sun, Solar atmosphere | ||||
Official Date: | March 2013 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Physics | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Nakariakov, V. M. (Valery M.) | ||||
Extent: | xiv, 146 leaves : illustrations. | ||||
Language: | eng |
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