Helioseismic detections of sunspot regions
Abstract/Contents
- Abstract
- Sunspots are regions where strong magnetic fields emerge from the solar interior and where major eruptive events occur. Sunspot studies are needed to understand the generation and emergence of magnetic fields in the photosphere and monitor the solar magnetic activity. In this thesis, local helioseismology methods are used to detect and study sunspot regions on the far-side of the Sun, the photosphere, and the deep convection zone, before these magnetic regions become visible on the solar disc. One of the successes of helioseismology is the imaging of solar far-side magnetic regions. Helioseismic holography and time-distance technique are capable of detecting sunspot regions on the far side of the sun and provide useful warnings for space weather forecasts. These techniques employ acoustic waves that travel to the far side and return to the front side after multiple bounces in the photosphere. We explore the possibility of far-side imaging by the time-distance technique using three-skip acoustic signals. This method is first validated with use of numerical simulation data and then it is used to detect sunspot regions on the solar far side using SOHO/MDI observations. It is shown that if these maps are combined with maps of existing methods, the appearance of spurious signals is reduced. Sunspot observations in the photosphere show that the acoustic power inside a sunspot region is significantly reduced compared to the quiet Sun. The power deficit is due to three main groups of physical mechanisms: absorption, emissivity reduction, and local suppression. These effects are separated with a measurement scheme that utilizes one- and double-skip waves in sunspots and quiet-sun regions. Using a large sample of sunspots observed with SOHO/MDI, the coefficients of each mechanism are measured as functions of travel distance and their relative contribution to the total power reduction is determined as well. The methods and the results of this study will be utilized for the detection of emerging sunspot regions in the convection zone. Helioseismic methods can be used to detect and study the properties of sunspot regions not only on the solar far side and the photosphere but also in the deep solar interior. We develop a measurement procedure which is capable of detecting emerging sunspot regions at depths around 60,000 km and 1-2 days before the detected magnetic structures emerge to the surface. The detection is based on measurements of the acoustic phase travel-time perturbations with the time-distance helioseismology technique using SOHO/MDI, SDO/HMI, and GONG datasets. The travel-time anomalies are related with cross-covariance frequency perturbations that depend strongly on the acoustic frequency. The implications of these measurements to studies of magnetic flux emergence in the solar convection zone and the potential applications to space weather forecasts are discussed.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2012 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Ilonidis, Efstathios |
|---|---|
| Associated with | Stanford University, Department of Physics |
| Primary advisor | Scherrer, Philip H |
| Thesis advisor | Scherrer, Philip H |
| Thesis advisor | Petrosian, Vahe |
| Thesis advisor | Zhao, Junwei |
| Advisor | Petrosian, Vahe |
| Advisor | Zhao, Junwei |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Stathis Ilonidis. |
|---|---|
| Note | Submitted to the Department of Physics. |
| Thesis | Ph.D. Stanford University 2012 |
| Location | electronic resource |
Access conditions
- Copyright
- © 2012 by Efstathios Ilonidis
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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