Fully Resolved Quiet-Sun Magnetic Flux Tube Observed With the Sunrise/Imax Instrument

Lagg, A.; Solanki, S. K.; Riethmüller, T. L.; Pillet, V. Martı́nez; Schüßler, M.; Hirzberger, J.; Feller, A.; Borrero, J. M.; Schmidt, Wolfgang; Iniesta, J. C. del Toro; Bonet, J. A.; Barthol, P.; Berkefeld, T.; Domingo, V.; Gandorfer, A.; Knölker, M.; Title, A. M.

doi:10.1088/2041-8205/723/2/l164

Cited by 111 publications

(120 citation statements)

References 18 publications

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“…Sect. 4.3) values of up to 80%, because under such an assumption this factor has to reproduce both the real stray light and the magnetic filling factor inside a pixel (but see also Lagg et al 2010;Martínez González et al 2012). Our choice of the inversion setup yields an acceptable fit to the Stokes I profiles (indicating a reasonable choice of α) while the polarization signal in Stokes QUV is less well reproduced because of our one-component assumption.…”

Section: Inversion Setupmentioning

confidence: 95%

Thermodynamic fluctuations in solar photospheric three-dimensional convection simulations and observations

Beck

Fabbian

Moreno‐Insertis

et al. 2013

A&A

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Context. Numerical three-dimensional (3D) radiative (magneto-)hydrodynamical [(M)HD] simulations of solar convection are nowadays used to understand the physical properties of the solar photosphere and convective envelope, and, in particular, to determine the Sun's photospheric chemical abundances. To validate this approach, it is important to check that no excessive thermodynamic fluctuations arise as a consequence of the partially incomplete treatment of radiative transfer causing radiative damping that is too modest. Aims. We investigate the realism of the thermodynamics in recent state-of-the-art 3D convection simulations of the solar atmosphere carried out with the Stagger code.Methods. We compared the characteristic properties of several Fe i lines (557.6 nm, 630 nm, 1565 nm) and one Si i line at 1082.7 nm in solar disc-centre observations of different spatial resolution with spectra synthesized from 3D convection simulations. The observations were taken with ground-based (Echelle spectrograph, Göttingen Fabry-Pérot Interferometer (GFPI), POlarimetric LIttrow Spectrograph, Tenerife Infrared Polarimeter, all at the Vacuum Tower Telescope on Tenerife) and space-based instruments (Hinode/Spectropolarimeter). We degraded the synthetic spectra to the spatial resolution of the observations, based on the distribution of the continuum intensity I c . We estimated the spectral degradation to be applied to the simulation results by comparing atlas spectra with averaged observed spectra. In addition to deriving a set of line parameters directly from the intensity profiles, we used the SIR (Stokes Inversion based on Response functions) code to invert the spectra. Results. The spatial degradation kernels yield a similar generic spatial stray-light contamination of about 30% for all instruments. The spectral stray light inside the different spectrometers is found to be between 2% and 20%. Most of the line parameters from the observational data are matched by the degraded HD simulation spectra. The inversions predict a macroturbulent velocity v mac below 10 m s −1 for the HD simulation spectra at full spatial resolution, whereas they yield v mac 1000 m s −1 at a spatial resolution of 0. 3. The temperature fluctuations in the inversion of the degraded HD simulation spectra do not exceed those from the observational data (of the order of 100−200 K rms for −2 log τ 500 nm −0.5). The comparison of line parameters in spatially averaged profiles with the averaged values of line parameters in spatially resolved profiles indicates a significant change in (average) line properties on a spatial scale between 0. 13 and 0. 3. Conclusions. Up to a spatial resolution of 0. 3 (GFPI spectra), we find no indications of excessive thermodynamic fluctuations in the 3D HD simulation. To definitely confirm that simulations without spatial degradation contain fully realistic thermodynamic fluctuations requires observations at even higher spatial resolution (i.e. <0. 13).

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Section: Inversion Setupmentioning

confidence: 95%

Thermodynamic fluctuations in solar photospheric three-dimensional convection simulations and observations

Beck

Fabbian

Moreno‐Insertis

et al. 2013

A&A

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“…Magnetic elements have diameters smaller than ≈350 km and exhibit field strengths of 1 to 2 kG (Stenflo 1973;Rabin 1992;Rüedi et al 1992). They are the chief magnetic constituents of faculae, which are bright (i.e., hotter than their surroundings) particularly in the mid-photosphere and above (see reviews by Solanki 1993;Solanki et al 2006) and are present even in the internetwork (Lagg et al 2010).…”

Section: Temporal Evolution Of the Magnetic Fieldmentioning

confidence: 99%

The magnetic field in the solar atmosphere

Wiegelmann

Thalmann

Solanki

2014

Astron Astrophys Rev

172

125

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This publication provides an overview of magnetic fields in the solar atmosphere with the focus lying on the corona. The solar magnetic field couples the solar interior with the visible surface of the Sun and with its atmosphere. It is also responsible for all solar activity in its numerous manifestations. Thus, dynamic phenomena such as coronal mass ejections and flares are magnetically driven. In addition, the field also plays a crucial role in heating the solar chromosphere and corona as well as in accelerating the solar wind. Our main emphasis is the magnetic field in the upper solar atmosphere so that photospheric and chromospheric magnetic structures are mainly discussed where relevant for higher solar layers. Also, the discussion of the solar atmosphere and activity is limited to those topics of direct relevance to the magnetic field. After giving a brief overview about the solar magnetic field in general and its global structure, we discuss in more detail the magnetic field in active regions, the quiet Sun and coronal holes.

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“…Alternatively, one could go one step further and argue that small-scale structures within magnetic concentration in the intergranular lanes could govern the loop width. Very small kilogauss flux tubes have been observed even in the quiet Sun [109]. These would provide enough magnetic flux for a whole coronal loop.…”

Section: (B) Structure Of Coronal Loopsmentioning

confidence: 99%

What can large-scale magnetohydrodynamic numerical experiments tell us about coronal heating?

Peter

2015

Phil. Trans. R. Soc. A.

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The upper atmosphere of the Sun is governed by the complex structure of the magnetic field. This controls the heating of the coronal plasma to over a million kelvin. Numerical experiments in the form of threedimensional magnetohydrodynamic simulations are used to investigate the intimate interaction between magnetic field and plasma. These models allow one to synthesize the coronal emission just as it would be observed by real solar instrumentation. Largescale models encompassing a whole active region form evolving coronal loops with properties similar to those seen in extreme ultraviolet light from the Sun, and reproduce a number of average observed quantities. This suggests that the spatial and temporal distributions of the heating as well as the energy distribution of individual heat deposition events in the model are a good representation of the real Sun. This provides evidence that the braiding of fieldlines through magneto-convective motions in the photosphere is a good concept to heat the upper atmosphere of the Sun.

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Fully Resolved Quiet-Sun Magnetic Flux Tube Observed With the Sunrise/Imax Instrument

Cited by 111 publications

References 18 publications

Thermodynamic fluctuations in solar photospheric three-dimensional convection simulations and observations

Thermodynamic fluctuations in solar photospheric three-dimensional convection simulations and observations

The magnetic field in the solar atmosphere

What can large-scale magnetohydrodynamic numerical experiments tell us about coronal heating?

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