Distribution functions for magnetic fields on the quiet Sun

Stenflo, J. O.

doi:10.1051/0004-6361/200913972

Cited by 81 publications

(169 citation statements)

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“…Finally, the degree of spatial coherence of the signals increases with the polarimetric signal. By this we mean that the weakest detected fluxes of the quiet Sun on scales below 1000 km show a very dynamic, intermittent, stochastic, magnetic activity unlike the "deterministic" characterisation of the magnetic structure of sunspots and other active structures formed by the socalled flux tubes (López Ariste et al 2006;Martínez González et al 2010b;Stenflo 2010). Stronger fluxes, but still two orders of magnitude weaker than those of the network regions, may organise at granular scales and form magnetic loops (e.g.…”

Section: Introductionmentioning

confidence: 99%

Inference of magnetic fields in the very quiet Sun

González

Yabar

Lagg

et al. 2016

A&A

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Context. Over the past 20 yr, the quietest areas of the solar surface have revealed a weak but extremely dynamic magnetism occurring at small scales (<500 km), which may provide an important contribution to the dynamics and energetics of the outer layers of the atmosphere. Understanding this magnetism requires the inference of physical quantities from high-sensitivity spectro-polarimetric data with high spatio-temporal resolution. Aims. We present high-precision spectro-polarimetric data with high spatial resolution (0.4 ) of the very quiet Sun at 1.56 µm obtained with the GREGOR telescope to shed some light on this complex magnetism. Methods. We used inversion techniques in two main approaches. First, we assumed that the observed profiles can be reproduced with a constant magnetic field atmosphere embedded in a field-free medium. Second, we assumed that the resolution element has a substructure with either two constant magnetic atmospheres or a single magnetic atmosphere with gradients of the physical quantities along the optical depth, both coexisting with a global stray-light component. Results. Half of our observed quiet-Sun region is better explained by magnetic substructure within the resolution element. However, we cannot distinguish whether this substructure comes from gradients of the physical parameters along the line of sight or from horizontal gradients (across the surface). In these pixels, a model with two magnetic components is preferred, and we find two distinct magnetic field populations. The population with the larger filling factor has very weak (∼150 G) horizontal fields similar to those obtained in previous works. We demonstrate that the field vector of this population is not constrained by the observations, given the spatial resolution and polarimetric accuracy of our data. The topology of the other component with the smaller filling factor is constrained by the observations for field strengths above 250 G: we infer hG fields with inclinations and azimuth values compatible with an isotropic distribution. The filling factors are typically below 30%. We also find that the flux of the two polarities is not balanced. From the other half of the observed quiet-Sun area ∼50% are two-lobed Stokes V profiles, meaning that 23% of the field of view can be adequately explained with a single constant magnetic field embedded in a non-magnetic atmosphere. The magnetic field vector and filling factor are reliable inferred in only 50% based on the regular profiles. Therefore, 12% of the field of view harbour hG fields with filling factors typically below 30%. At our present spatial resolution, 70% of the pixels apparently are non-magnetised.

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Section: Introductionmentioning

confidence: 99%

Inference of magnetic fields in the very quiet Sun

González

Yabar

Lagg

et al. 2016

A&A

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“…In addition to Martínez González et al (2008), a number of works have also argued in favor of an isotropic distribution of magnetic fields in the internetwork. In particular, Asensio Ramos (2009) and Stenflo (2010), employing two different approaches, both concluded that for very weak magnetic fields (B → 0) the distribution becomes isotropic. With our present data we cannot argue against or in favor of this interpretation.…”

Section: Discussionmentioning

confidence: 99%

“…This has led to a new controversy about the angular distribution of the magnetic field vector in the quiet Sun. While some authors (Orozco Suárez et al 2007a,b;Lites et al 2007Lites et al , 2008 found that the magnetic field is mostly horizontal (γ ≈ 90 • ; with γ being the inclination of the magnetic field vector with respect to the observer's line-of-sight), others favor a quasi-isotropic distribution of magnetic fields (Martínez González et al 2008;Asensio Ramos 2009;Stenflo 2010). With a few exceptions (Harvey et al 2007;Lites et al 2008;Martínez González et al 2008), all previous studies were carried out employing data recorded at disk center only.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, Asensio Ramos (2009), Stenflo (2010), and Borrero & Kobel (2011;hereafter Paper I) warned that the highly inclined magnetic fields obtained by some studies could be caused by the noise in the linear polarization profiles. This yields a distribution of B ⊥ (component of the magnetic field vector that is perpendicular to the observer's line-of-sight) with a peak at around 50-90 Gauss.…”

Section: Introductionmentioning

confidence: 99%

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Inferring the magnetic field vector in the quiet Sun

Borrero

Kobel

2013

A&A

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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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“…whether they are created by local dynamo processes. The answer to the long-standing question of whether smallscale magnetic fields are more horizontal or vertical seems to currently depend on the method of analysis, and especially how the noise in Q and U is dealt with (e.g., Lites et al 2008;Asensio Ramos 2009;Stenflo 2010;Borrero & Kobel 2011;Orozco Suárez & Bellot Rubio 2012;Steiner & Rezaei 2012;Martínez Pillet 2013). Because the signals Fig.…”

Section: The Need For Large Aperturesmentioning

confidence: 99%

Prospects of Solar Magnetometry—From Ground and in Space

Kleint¹,

Gandorfer²

2015

Space Sci Rev

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In this review we present an overview of observing facilities for solar research, which are planned or will come to operation in near future. We concentrate on facilities, which harbor specific potential for solar magnetometry. We describe the challenges and science goals of future magnetic measurements, the status of magnetic field measurements at different major solar observatories, and provide an outlook on possible upgrades of future instrumentation.

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Distribution functions for magnetic fields on the quiet Sun

Cited by 81 publications

References 41 publications

Inference of magnetic fields in the very quiet Sun

Inference of magnetic fields in the very quiet Sun

Inferring the magnetic field vector in the quiet Sun

Prospects of Solar Magnetometry—From Ground and in Space

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