Numerical Models of Travel-Time Inhomogeneities in Sunspots

Moradi, Hamed; Hanasoge, Shravan M.; Cally, Paul Stuart

doi:10.1088/0004-637x/690/1/l72

Cited by 40 publications

(60 citation statements)

References 24 publications

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“…A number of simulations (e.g. Cameron, Gizon, and Daiffallah, 2007;Cameron, Gizon, and Duvall, 2008;Hanasoge, 2008;Moradi, Hanasoge, and Cally, 2009;Rempel, Schüssler, and Knölker, 2009a) apply an Alfvén wave-speed limiter to moderate the action of the Lorentz forces, thereby indirectly controlling the plasma-β. Having described this context, three rather serious issues remain as yet outstanding: i) What are the spatiotemporal resolution requirements for simulating waves in an MHD environment?…”

Section: Methodsmentioning

confidence: 99%

“…Braun and Birch, 2008;Birch et al, 2009;Gizon et al, 2009aGizon et al, , 2009b) and significant advances have also been made in the simulation of helioseismic wave propagation in magnetized plasmas (see e.g. Cameron, Gizon, and Daiffallah, 2007;Parchevsky and Kosovichev, 2007;Cameron, Gizon, and Duvall, 2008;Hanasoge, 2008;Moradi, Hanasoge, and Cally, 2009;Parchevsky and Kosovichev, 2009;Shelyag et al, 2009;Cameron et al, 2010).…”

Section: Why Sunspots Are Interestingmentioning

confidence: 99%

“…Cameron, Gizon, and Daiffallah, 2007;Cameron, Gizon, and Duvall, 2008;Moradi, Hanasoge, and Cally, 2009). This approach bypasses the need for linear forward models (i.e.…”

Section: Diagnostics Potential Of Helioseismologymentioning

confidence: 99%

“…The SPARC code has been utilized to study wave propagation through model sunspots (e.g. Hanasoge, 2008;Moradi, Hanasoge, and Cally, 2009;Moradi and Hanasoge, 2010), as well as solar convection (Hanasoge, Duvall, and DeRosa, 2010a).…”

Section: The Sparc Codementioning

confidence: 99%

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Modeling the Subsurface Structure of Sunspots

et al. 2010

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While sunspots are easily observed at the solar surface, determining their subsurface structure is not trivial. There are two main hypotheses for the subsurface structure of sunspots: the monolithic model and the cluster model. Local helioseismology is the only means by which we can investigate subphotospheric structure. However, as current linear inversion techniques do not yet allow helioseismology to probe the internal structure with sufficient confidence to distinguish between the monolith and cluster models, the development of physically realistic sunspot models are a priority for helioseismologists. This is because they are not only important indicators of the variety of physical effects that may influence helioseismic inferences in active regions, but they also enable detailed assessments of the validity of helioseismic interpretations through numerical forward modeling. In this article, we provide a critical review of the existing sunspot models and an overview of numerical methods employed to model wave propagation through model sunspots. We then carry out a helioseismic analysis of the sunspot in Active Region 9787 and address the serious inconsistencies uncovered by Gizon et al. (2009aGizon et al. ( , 2009b. We find that this sunspot is most probably associated with a shallow, positive wave-speed perturbation (unlike the traditional two-layer model) and that travel-time measurements are consistent with a horizontal outflow in the surrounding moat.

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Section: Methodsmentioning

confidence: 99%

Section: Why Sunspots Are Interestingmentioning

confidence: 99%

“…Cameron, Gizon, and Daiffallah, 2007;Cameron, Gizon, and Duvall, 2008;Moradi, Hanasoge, and Cally, 2009). This approach bypasses the need for linear forward models (i.e.…”

Section: Diagnostics Potential Of Helioseismologymentioning

confidence: 99%

Section: The Sparc Codementioning

confidence: 99%

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Modeling the Subsurface Structure of Sunspots

et al. 2010

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“…In our final set of experiments, we ascertain the contribution of the underlying thermal perturbations to the traveltime shifts in contrast to the direct magnetic effects in a sunspot with surface field strength of 1.5 kG and a Wilson depression of 400 km. As shown in Moradi & Cally (2008) and Moradi, Hanasoge & Cally (2009) this can easily be achieved in linear numerical simulations by suppressing the direct magnetic effect on the waves. The combined outcomes from these experiments provide us with valuable diagnostics of both the thermal and magnetic structures of sunspots.…”

Section: The Background Modelmentioning

confidence: 95%

Directional time–distance probing of model sunspot atmospheres

Moradi

Cally

Przybylski

et al. 2015

Monthly Notices of the Royal Astronomical Society

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A crucial feature not widely accounted for in local helioseismology is that surface magnetic regions actually open a window from the interior into the solar atmosphere, and that the seismic waves leak through this window, reflect high in the atmosphere, and then re-enter the interior to rejoin the seismic wave field normally confined there. In a series of recent numerical studies using translation invariant atmospheres, we utilised a "directional time-distance helioseismology" measurement scheme to study the implications of the returning fast and Alfvén waves higher up in the solar atmosphere on the seismology at the photosphere Moradi & Cally 2014). In this study, we extend our directional time-distance analysis to more realistic sunspot-like atmospheres to better understand the direct effects of the magnetic field on helioseismic travel-time measurements in sunspots. In line with our previous findings, we uncover a distinct frequency-dependant directional behaviour in the travel-time measurements, consistent with the signatures of MHD mode conversion. We found this to be the case regardless of the sunspot field strength or depth of its Wilson depression. We also isolated and analysed the direct contribution from purely thermal perturbations to the measured travel times, finding that waves propagating in the umbra are much more sensitive to the underlying thermal effects of the sunspot.

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