Sunspot seismic halos generated by fast MHD wave refraction

Khomenko, E.; Collados, M.

doi:10.1051/0004-6361/200913030

Cited by 48 publications

(63 citation statements)

References 27 publications

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“…that the fluid flows along field lines. Khomenko and Collados (2006) used the Pizzo (1986) sunspot model in numerical simulations of magnetoacoustic wave propagation, and more recently Khomenko and Collados (2008) produced a new set of models consisting of concatenation of self-similar models in the deep layers, where the gas pressure dominates over magnetic pressure, with models in which the pressure distribution is prescribed on the axis. In the deep photospheric layers, a self-similar solution for the magnetic field is calculated following the method of Low (1980), while the pressure and density distributions with height and radius are found from analytical expressions.…”

Section: Solution Of Full Mhs Force Balancementioning

confidence: 99%

“…The IAC MHD code, described by Khomenko and Collados (2006) and Khomenko, Collados, and Felipe (2008), solves the non-linear MHD equations for perturbations, written in the conservative form, using a fourth-order central difference scheme and advanced in time by a fourth-order Runge -Kutta method. In a similar manner to Stein and Nordlund (1998) and Caunt and Korpi (2001), in order to damp high-frequency numerical noise on subgrid scales, the physical diffusive terms in the equations of momentum and energy are replaced by artificial equivalents.…”

Section: The Iac Mhd Codementioning

confidence: 99%

“…For the best results, 10 to 15 grid points are allocated to the PML layer. This code has been used to study the wave propagation and refraction in a small sunspot (Khomenko and Collados, 2006); non-linear wave propagation, shock formation, mode conversion, and energy transport in small-scale flux tubes with internal structure (Khomenko, Collados, and Felipe, 2008).…”

Section: The Iac Mhd 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: Solution Of Full Mhs Force Balancementioning

confidence: 99%

Section: The Iac Mhd Codementioning

confidence: 99%

Section: The Iac Mhd Codementioning

confidence: 99%

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Modeling the Subsurface Structure of Sunspots

et al. 2010

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“…This dependence is expressed in terms of the Abel integral equation (89), which can be solved analytically.…”

Section: General Helioseismic Inverse Problemmentioning

confidence: 99%

Advances in Global and Local Helioseismology: An Introductory Review

Kosovichev

2011

The Pulsations of the Sun and the Stars

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Abstract. Helioseismology studies the structure and dynamics of the Sun's interior by observing oscillations on the surface. These studies provide information about the physical processes that control the evolution and magnetic activity of the Sun. In recent years, helioseismology has made substantial progress towards the understanding of the physics of solar oscillations and the physical processes inside the Sun, thanks to observational, theoretical and modeling efforts. In addition to the global seismology of the Sun based on measurements of global oscillation modes, a new field of local helioseismology, which studies oscillation travel times and local frequency shifts, has been developed. It is capable of providing 3D images of the subsurface structures and flows. The basic principles, recent advances and perspectives of global and local helioseismology are reviewed in this article.

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“…It is, generally, suggested that this enhancement is due to the interaction of acoustic waves with the canopy. There exist, in the literature, several mechanisms that try to explain the details of the nature of the observed enhancement (Carlsson & Bogdan 2006;Hanasoge et al 2009;Khomenko & Collados 2009;Kuridze et al 2008Kuridze et al , 2009Jacoutot et al 2009). …”

Section: Introductionmentioning

confidence: 99%

Oscillations in a network region observed in the Hαline and their relation to the magnetic field

Kontogiannis

Tsiropoula

Tziotziou

et al. 2010

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Aims. Our aim is to gain a better understanding of the interaction between acoustic oscillations and the small-scale magnetic fields of the Sun. To this end, we examine the oscillatory properties of a network region and their relation to the magnetic configuration of the chromosphere. We link the oscillatory properties of a network region and their spatial variation with the variation of the parameters of the magnetic field. We investigate the effect of the magnetic canopy and the diverging flux tubes of the chromospheric network on the distribution of oscillatory power over the network and internetwork. Methods. We use a time series of high resolution filtergrams at five wavelengths along the Hα profile observed with the Dutch Open Telescope, as well as high resolution magnetograms taken by the SOT/SP onboard HINODE. Using wavelet analysis, we construct power maps of the 3, 5 and 7 min oscillations of the Doppler signals calculated at ±0.35 Å and ±0.7 Å from the Hα line center. These represent velocities at chromospheric and photospheric levels respectively. Through a current-free (potential) field extrapolation we calculate the chromospheric magnetic field and compare its morphology with the Hα filtergrams. We calculate the plasma β and the magnetic field inclination angle and compare their distribution with the oscillatory power at the 3, 5 and 7 min period bands. Results. Chromospheric mottles seem to outline the magnetic field lines. The Hα ± 0.35 Å Doppler signals are formed above the canopy, while the Hα ± 0.7 Å corresponding ones below it. The 3 min power is suppressed at the chromosphere around the network, where the canopy height is lower than 1600 km, while at the photosphere it is enhanced due to reflection. 3, 5 and 7 min oscillatory power is increased around the network at the photosphere due to reflection of waves on the overlying canopy, while increased 5 and 7 min power at the chromosphere is attributed mainly to wave refraction on the canopy. At these high periods, power is also increased due to p-mode leakage because of the high inclinations of the magnetic field. Conclusions. Our high resolution Hα observations and photospheric magnetograms provide the opportunity to highlight the details of the interaction between acoustic oscillations and the magnetic field of a network region. We conclude that several mechanisms that have been proposed such as p-mode leakage, mode conversion, reflection and refraction of waves on the magnetic canopy may act together and result to the observed properties of network oscillations.

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Sunspot seismic halos generated by fast MHD wave refraction

Cited by 48 publications

References 27 publications

Modeling the Subsurface Structure of Sunspots

Modeling the Subsurface Structure of Sunspots

Advances in Global and Local Helioseismology: An Introductory Review

Oscillations in a network region observed in the Hαline and their relation to the magnetic field

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