Resolving the Internal Magnetic Structure of the Solar Network

González, M. J. Martínez; Rubio, L. R. Bellot; Solanki, S. K.; Pillet, V. Martı́nez; Iniesta, J. C. del Toro; Barthol, P.; Schmidt, Wolfgang

doi:10.1088/2041-8205/758/2/l40

Cited by 38 publications

(34 citation statements)

References 27 publications

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“…Many magnetic canopies were found to lie above essentially field free regions. The canopies found here agree with the model proposed by Grossmann-Doerth et al (1988) for the production of the Stokes V area asymmetry and the observational results presented by Rezaei et al (2007), Narayan &Scharmer (2010) andMartínez González et al (2012). All magnetic features were observed to expand with height and many isolated MFCs merged to form comparatively large expanses of magnetic field at log(τ) = −2.3.…”

Section: Discussionsupporting

confidence: 90%

Properties of solar plage from a spatially coupled inversion of Hinode SP data

Buehler

Lagg

Solanki

et al. 2015

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Aims. The properties of magnetic fields forming an extended plage region in AR 10953 were investigated. Methods. Stokes spectra of the Fe I line pair at 6302 Å recorded by the spectropolarimeter aboard the Hinode satellite were inverted using the SPINOR code. The code performed a 2D spatially coupled inversion on the Stokes spectra, allowing the retrieval of gradients in optical depth within the atmosphere of each pixel, whilst accounting for the effects of the instrument's PSF. Consequently, no magnetic filling factor was needed.Results. The inversion results reveal that plage is composed of magnetic flux concentrations (MFCs) with typical field strengths of 1520 G at log(τ) = −0.9 and inclinations of 10 • −15 • . The MFCs expand by forming magnetic canopies composed of weaker and more inclined magnetic fields. The expansion and average temperature stratification of isolated MFCs can be approximated well with an empirical plage thin flux tube model. The highest temperatures of MFCs are located at their edges in all log(τ) layers. Whilst the plasma inside MFCs is nearly at rest, each is surrounded by a ring of downflows of on average 2.4 km s −1 at log(τ) = 0 and peak velocities of up to 10 km s −1 , which are supersonic. The downflow ring of an MFC weakens and shifts outwards with height, tracing the MFC's expansion. Such downflow rings often harbour magnetic patches of opposite polarity to that of the main MFC with typical field strengths below 300 G at log(τ) = 0. These opposite polarity patches are situated beneath the canopy of their main MFC. We found evidence of a strong broadening of the Stokes profiles in MFCs and particularly in the downflow rings surrounding MFCs (expressed by a microturbulence in the inversion). This indicates the presence of strong unresolved velocities. Larger magnetic structures such as sunspots cause the field of nearby MFCs to be more inclined.

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Section: Discussionsupporting

confidence: 90%

Properties of solar plage from a spatially coupled inversion of Hinode SP data

Buehler

Lagg

Solanki

et al. 2015

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“…Flux tubes expand with height owing to pressure balance and magnetic flux conservation. Martínez González et al (2012) also analyzed IMaX L12 data of a single network element and found evidence for a canopy. By studying a statistical ensemble of BPs, mostly consisting of internetwork elements, we were able to show that the spatial distribution of the asymmetry is consistent with the presence of a canopy, thus further supporting the model of Grossmann-Doerth et al (1988) and Solanki (1989).…”

Section: Discussionmentioning

confidence: 99%

“…This situation has changed with the availability of data recorded by the Sunrise balloon-borne observatory, which have allowed magnetic elements even in the internetwork quiet Sun to be spatially resolved (Lagg et al 2010) and have allowed the internal structure of network magnetic features to be probed (Martínez González et al 2012) providing a good opportunity to revisit BPs and to compare their observational properties with predictions from state-of-the-art radiation magnetohydrodynamic (MHD) simulations.…”

Section: Introductionmentioning

confidence: 99%

Comparison of solar photospheric bright points between Sunrise observations and MHD simulations

Riethmüller

Solanki

Berdyugina

et al. 2014

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Bright points (BPs) in the solar photosphere are thought to be the radiative signatures (small-scale brightness enhancements) of magnetic elements described by slender flux tubes or sheets located in the darker intergranular lanes in the solar photosphere. They contribute to the ultraviolet (UV) flux variations over the solar cycle and hence may play a role in influencing the Earth's climate. Here we aim to obtain a better insight into their properties by combining high-resolution UV and spectro-polarimetric observations of BPs by the Sunrise Observatory with 3D compressible radiation magnetohydrodynamical (MHD) simulations. To this end, full spectral line syntheses are performed with the MHD data and a careful degradation is applied to take into account all relevant instrumental effects of the observations. In a first step it is demonstrated that the selected MHD simulations reproduce the measured distributions of intensity at multiple wavelengths, line-of-sight velocity, spectral line width, and polarization degree rather well. The simulated line width also displays the correct mean, but a scatter that is too small. In the second step, the properties of observed BPs are compared with synthetic ones. Again, these are found to match relatively well, except that the observations display a tail of large BPs with strong polarization signals (most likely network elements) not found in the simulations, possibly due to the small size of the simulation box. The higher spatial resolution of the simulations has a significant effect, leading to smaller and more numerous BPs. The observation that most BPs are weakly polarized is explained mainly by the spatial degradation, the stray light contamination, and the temperature sensitivity of the Fe i line at 5250.2 Å. Finally, given that the MHD simulations are highly consistent with the observations, we used the simulations to explore the properties of BPs further. The Stokes V asymmetries increase with the distance to the center of the mean BP in both observations and simulations, consistent with the classical picture of a production of the asymmetry in the canopy. This is the first time that this has been found also in the internetwork. More or less vertical kilogauss magnetic fields are found for 98% of the synthetic BPs underlining that basically every BP is associated with kilogauss fields. At the continuum formation height, the simulated BPs are on average 190 K hotter than the mean quiet Sun, the mean BP field strength is found to be 1750 G, and the mean inclination is 17 • , supporting the physical flux-tube paradigm to describe BPs. On average, the synthetic BPs harbor downflows increasing with depth. The origin of these downflows is not yet understood very well and needs further investigation.

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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: 96%

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

Beck

Fabbian

Moreno‐Insertis

et al. 2013

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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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Resolving the Internal Magnetic Structure of the Solar Network

Cited by 38 publications

References 27 publications

Properties of solar plage from a spatially coupled inversion of Hinode SP data

Properties of solar plage from a spatially coupled inversion of Hinode SP data

Comparison of solar photospheric bright points between Sunrise observations and MHD simulations

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

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