The Horizontal Internetwork Magnetic Field: Numerical Simulations in Comparison to Observations with
                    <i>Hinode</i>

Steiner, O.; Rezaei, Reza; Schaffenberger, W.; Wedemeyer, Sven

doi:10.1086/589740

Cited by 86 publications

(130 citation statements)

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“…OR07 measured a fraction of 630 nm profiles of 87% and 35.5% that had a polarization degree of 3 and 4.5 times the noise level of about 1 × 10 −3 in their HINODE data. These numbers thus all agree that the area fraction covered by magnetic fields or exhibiting polarization signal should be above 50%, but calculation, we derived the same fraction of profiles with p > p thresh from spectra of 1564.8 nm synthesized from a simulation run with the Co 5 bold code described in Schaffenberger et al (2005Schaffenberger et al ( , 2006 and previously used in Steiner et al (2008). The snapshot was taken from the h20 run with an initial homogeneous horizontal magnetic field of 20 G. The simulation box corresponded to a 6.…”

Section: Discussionsupporting

confidence: 71%

“…Since the data properties (spatial scales of observed structures, pixels with significant polarization signal) and the inversion results (magnetic filling fraction, relation to granules/IGLs) seem to agree roughly with the HINODE data and their analysis in OR07 and LI08, we ascribe the reversal in the ratio of transversal to longitudinal fields (HINODE data: 5, IR data: 0.42) to: a) the different formation height of the spectral lines, and b) the analysis methods, i.e., either inversions using the ME approximation or a consistent treatment of thermodynamics (SIR), or calibration from integrated polarization signal to magnetic flux. We conclude that the issue would be investigated most effectively with simultaneous IR/VIS data, since simulations predict a strong dependence of the ratio on geometrical height (Steiner et al 2008). Although the existence of a significant fraction of inclined magnetic fields is confirmed by the present IR observations, their influence on the dynamics of the solar atmosphere remains unclear.…”

Section: Discussionmentioning

confidence: 71%

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The magnetic flux of the quiet Sun internetwork as observed with the Tenerife infrared polarimeter

Beck¹,

Rezaei²

2009

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Context. Observations made with the spectropolarimeter onboard the HINODE satellite have detected abundant horizontal magnetic fields in the internetwork quiet Sun. Aims. We compare the results for the horizontal fields obtained at 630 nm with ground-based observations at 1.56 μm, where the sensitivity to magnetic fields is higher than in the visible. Methods. We obtained 30-s integrated spectropolarimetric data of the quiet Sun on disc centre during a period of extremely stable and good seeing. The data have a rms noise in polarization of around 2 × 10 −4 of the continuum intensity. The low noise level allows the spectra to be inverted with the SIR code. We compare the inversion results with proxies to determine the magnetic flux. Results. We confirm the presence of the horizontal fields in the quiet Sun internetwork as reported for the satellite data, including voids without linear polarization signal that extend over an area of a few granules. Voids in the circular polarization signal are only of granular scale. More than 60% of the surface show polarization signals of above four times the rms noise level. We find that the total magnetic flux contained in the more inclined to horizontal fields (γ > 45 • ) is lower by a factor of around 2 than that of the less inclined fields. The proxies for flux determination are strongly affected by the thermodynamic state of the atmosphere, and hence, seem to be unreliable. Conclusions. During spells of good seeing conditions, adaptive optics can render ground-based slit-spectrograph observations at a 70-cm telescope equivalent to the seeing-free space-based data of half-meter class telescopes. We suggest that the difference in the ratio of horizontal to transversal flux between the ground-based infrared data and the satellite-based visible data is due to the different formation heights of the respective spectral lines. We emphasize that the true amount of magnetic flux cannot be derived directly from the spectra. For purely horizontal flux, one would need its vertical extension that has to be estimated by explicit modeling, using the observed spectra as boundary conditions, or be taken from MHD simulations. Time-series of the evolution of the magnetic flux and chromospheric diagnostics are needed to address its possible contribution to chromospheric heating.

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Section: Discussionsupporting

confidence: 71%

Section: Discussionmentioning

confidence: 71%

The magnetic flux of the quiet Sun internetwork as observed with the Tenerife infrared polarimeter

Beck¹,

Rezaei²

2009

A&A

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“…Overturning convection would instead expel a magnetic field that is imposed from above, through the well-known process of convective expulsion (Zel'dovich, 1956;Weiss, 1966). The process is seen in action in numerical simulations of horizontal magnetic fields overlying granulation by Steiner et al (2008Steiner et al ( , 2009.…”

Section: Sunspot Structure: a Critical Assessment Of Existing Modelsmentioning

confidence: 99%

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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“…Since the Stokes profiles sample increasingly higher atmospheric layers as the heliocentric angle increases, the distribution of the magnetic field vector can be different for different values of Θ, even if the probability distribution of the magnetic field vector is the same at all positions on the solar disk at a fixed geometrical depth. All these effects could be properly accounted for by means of 3D MHD simulations of the solar photosphere (Schüssler & Vögler 2008;Steiner et al 2008Steiner et al , 2009Danilovic et al 2010). …”

Section: Discussionmentioning

confidence: 99%

Inferring the magnetic field vector in the quiet Sun

Borrero

Kobel

2013

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Recent investigations of the magnetic field vector properties in the solar internetwork have provided diverging results. While some works found that the internetwork is mostly pervaded by horizontal magnetic fields, other works argued in favor of an isotropic distribution of the magnetic field vector. Motivated by these seemingly contradictory results and by the fact that most of these works have employed spectropolarimetric data at disk center only, we have revisited this problem employing high-quality data (noise level σ ≈ 3 × 10 −4 in units of the quiet-Sun intensity) at different latitudes recorded with the Hinode/SP instrument. Instead of applying traditional inversion codes of the radiative transfer equation to retrieve the magnetic field vector at each spatial point on the solar surface and studying the resulting distribution of the magnetic field vector, we surmised a theoretical distribution function of the magnetic field vector and used it to obtain the theoretical histograms of the Stokes profiles. These histograms were then compared to the observed ones. Any mismatch between them was ascribed to the theoretical distribution of the magnetic field vector, which was subsequently modified to produce a better fit to the observed histograms. With this method we find that Stokes profiles with signals above 2 × 10 −3 (in units of the continuum intensity) cannot be explained by an isotropic distribution of the magnetic field vector. We also find that the differences between the histograms of the Stokes profiles observed at different latitudes cannot be explained in terms of line-of-sight effects. However, they can be explained by a distribution of the magnetic field vector that inherently varies with latitude. We note that these results are based on a series of assumptions that, although briefly discussed in this paper, need to be considered in more detail in the future.

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The Horizontal Internetwork Magnetic Field: Numerical Simulations in Comparison to Observations with Hinode

Cited by 86 publications

References 14 publications

The magnetic flux of the quiet Sun internetwork as observed with the Tenerife infrared polarimeter

The magnetic flux of the quiet Sun internetwork as observed with the Tenerife infrared polarimeter

Modeling the Subsurface Structure of Sunspots

Inferring the magnetic field vector in the quiet Sun

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