Probing the Solar Interior in Three Dimensions
Abstract
The ability to probe the solar interior with sound waves has opened a vast domain of applications in solar, stellar, and fundamental physics. Helioseismology has enabled us to test and refine the standard solar model, and also to explore phenomena that we do not understand at all. In this talk I will discuss two topics in local helioseismology: solar near-surface convection and sunspots.
First, I will present recent inversions of helioseismic travel times (MDI/SOHO observations), which describe the plasma flow in the top 4 Mm of the convection zone. For daily averages, the flows are mostly horizontal and dominated by supergranulation. The inferred vertical flows are not unreasonable: upward flows are typically found in regions of horizontal outflows, with amplitudes that are consistent with mass conservation. A statistical study reveals other subtle effects, such as the influence of the Coriolis force on the flows. Second, I will comment on sunspot seismology, which offers unique prospects for studying the subsurface structure, formation, and evolution of sunspots. Solar waves are known to interact strongly with sunspots, as seen for example in the correlations of the random wave field at the solar surface. Because the effects of the magnetic field on the waves cannot be assumed to be weak, it is however a challenge to interpret the observations. I will argue that three-dimensional numerical simulations of wave propagation through sunspot models are an essential tool to help solve this problem. I will show an example of a simple sunspot model for which the numerical simulations mostly agree with the seismic observations. With the continued operations of SOHO and dedicated ground-based facilities, the upcoming launch of the Solar Dynamics Observatory of NASA, and the preparations for the Solar Orbiter mission of ESA, helioseismology is, today, a very active branch of solar physics.- Publication:
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AAS/Solar Physics Division Meeting #40
- Pub Date:
- May 2009
- Bibcode:
- 2009SPD....40.0201G