Global-mode helioseismology : extensions of a well-used method
Abstract/Contents
- Abstract
- Global-mode helioseismology has been used extensively to precisely infer the detailed properties of the solar interior. Multiple algorithms have been applied to several different datasets, which now span over two solar cycles. This dissertation deals primarily with two instruments, namely the Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory, and the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory. For MDI, we have two velocity datasets spanning the 15 years from 1996 to 2011: high-resolution images which were taken for a few months each year, and low-resolution images which were taken almost all the time. For HMI, we have even higher resolution velocity images taken since 2010. Unlike MDI, HMI also provides intensity data. The initial motivation for this study was to address known systematic errors in the analysis of MDI data, as well as discrepancies with inferences drawn by other projects, most notably the Global Oscillation Network Group. In particular, the MDI results indicated a high-latitude peak in the solar rotation rate, which is now believed to be spurious. Also, certain fits resulted in normalized residuals that indicate the fit is not using the correct model. Lastly, MDI saw an annual periodicity in frequency shifts, which can only be because of errors in geometry. Now that MDI is no longer operating, it has also become important to achieve continuity between the MDI and HMI datasets. To that end, both have been processed in their entirety using the same set of software. Since the original software was written when computational capabilities were far less than now, this involved the application of several updates. At the same time, we have adopted better models of the physics behind the oscillations and applied various geometric corrections. In this dissertation we investigate how these changes affected the global-mode parameters from the MDI analysis and the systematic errors therein. We then apply the fully updated analysis to the HMI data, and make a comparison of mode parameters derived from the various datasets from the two instruments. We find methods that decrease or eliminate the systematic errors mentioned above. Hence, inferences of the Sun's interior rotation have become more robust. Further, the comparison between MDI and HMI encourages the concatenation of their datasets, which may allow for the detection of new oscillation modes.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2016 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Larson, Tim |
|---|---|
| Associated with | Stanford University, Department of Physics. |
| Primary advisor | Scherrer, Philip H |
| Thesis advisor | Scherrer, Philip H |
| Thesis advisor | Church, Sarah Elizabeth |
| Thesis advisor | Schou, Jesper, (Scientist) |
| Advisor | Church, Sarah Elizabeth |
| Advisor | Schou, Jesper, (Scientist) |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Tim Larson. |
|---|---|
| Note | Submitted to the Department of Physics. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2016. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2016 by Timothy Paul Larson
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