Measurement and interpretation of travel-time shifts in the context of time-distance helioseismic detection of meridional flow
Abstract/Contents
- Abstract
- The role of meridional flow in maintaining the solar dynamo and differential rotation in the solar convection zone is not well understood and is currently under scrutiny. Traditional flux-transport dynamo models have posited the well known single-cell meridional flow with poleward flow at the photosphere and equatorward flow near the base of the convection zone. However, recent investigations seem to be revealing a discrepant picture of meridional flow which is at least double celled in the radial direction. In this work standard time-distance helioseismic techniques are modified and used to probe the solar convection zone to accurately determine the structure of meridional circulation. Helioseismology is a powerful tool for measuring the structure and flows on the solar surface and within the solar interior. It uses the photospherically visible aspect of (acoustic, surface-gravity) waves, that propagate and interfere throughout the Sun to form standing oscillation modes, as probes to make inferences about the structure and flows on the solar surface and interior. Time-distance helioseismology is based on measuring the travel-times of wave-packets moving between distinct points on the solar surface. Specifically, travel-time shifts obtained by calculating the difference in the travel-times of counter-propagating waves between pairs of points on the solar surface yield information about flows throughout the Sun. In this work time-distance helioseismic techniques are applied on artificial as well as solar velocity images to detect travel-time shift signals due to meridional flow, and modifications are suggested to enhance the signal-to-noise ratio of travel-time shift measurements. The artificial datacubes are constructed by embedding various meridional flow models in 3D acoustic wave propagation simulators, which are then used to discuss the interpretation of travel-time shifts, so that in the future an inversion procedure may be designed to accurately calculate meridional flow velocities. The solar data is obtained from the Helioseismic and Magnetic Imager (HMI) instrument aboard the Solar Dynamics Observatory (SDO) spacecraft and is used to measure travel-time shifts due to meridional flow in the solar convection zone non-standard helioseismic techniques. The issue of a systematic error dubbed as the "center-to-limb" effect that contaminates the travel-time shift measurements of solar meridional flow is also addressed in this work.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2015 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Chakraborty, Sudeepto |
|---|---|
| Associated with | Stanford University, Department of Electrical Engineering. |
| Primary advisor | Scherrer, Philip H |
| Thesis advisor | Scherrer, Philip H |
| Thesis advisor | Duvall, Thomas Lee |
| Thesis advisor | Zebker, Howard A |
| Advisor | Duvall, Thomas Lee |
| Advisor | Zebker, Howard A |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Sudeepto Chakraborty. |
|---|---|
| Note | Submitted to the Department of Electrical Engineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2015. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2015 by Sudeepto Chakraborty
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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