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Title: Magneto-static Modeling from Sunrise/IMaX: Application to an Active Region Observed with Sunrise II

Abstract

Magneto-static models may overcome some of the issues facing force-free magnetic field extrapolations. So far they have seen limited use and have faced problems when applied to quiet-Sun data. Here we present a first application to an active region. We use solar vector magnetic field measurements gathered by the IMaX polarimeter during the flight of the Sunrise balloon-borne solar observatory in 2013 June as boundary conditions for a magneto-static model of the higher solar atmosphere above an active region. The IMaX data are embedded in active region vector magnetograms observed with SDO /HMI. This work continues our magneto-static extrapolation approach, which was applied earlier to a quiet-Sun region observed with Sunrise I. In an active region the signal-to-noise-ratio in the measured Stokes parameters is considerably higher than in the quiet-Sun and consequently the IMaX measurements of the horizontal photospheric magnetic field allow us to specify the free parameters of the model in a special class of linear magneto-static equilibria. The high spatial resolution of IMaX (110–130 km, pixel size 40 km) enables us to model the non-force-free layer between the photosphere and the mid-chromosphere vertically by about 50 grid points. In our approach we can incorporate some aspects of themore » mixed beta layer of photosphere and chromosphere, e.g., taking a finite Lorentz force into account, which was not possible with lower-resolution photospheric measurements in the past. The linear model does not, however, permit us to model intrinsic nonlinear structures like strongly localized electric currents.« less

Authors:
; ; ; ; ; ; ;  [1];  [2];  [3];  [4]; ;  [5];  [6];  [7];  [8]
  1. Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, D-37077 Göttingen (Germany)
  2. School of Mathematics and Statistics, University of St. Andrews, St. Andrews KY16 9SS (United Kingdom)
  3. Astronomical Institute, AV CR, Fricova 298, 25165 Ondrejov (Czech Republic)
  4. Grupo de Astronomía y Ciencias del Espacio, Universidad de Valencia, E-46980 Paterna, Valencia (Spain)
  5. Instituto de Astrofísica de Andalucía (CSIC), Apartado de Correos 3004, E-18080 Granada (Spain)
  6. Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, D-79104 Freiburg (Germany)
  7. National Solar Observatory, 3665 Discovery Drive, Boulder, CO 80303 (United States)
  8. High Altitude Observatory, National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307-3000 (United States)
Publication Date:
OSTI Identifier:
22661238
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal, Supplement Series; Journal Volume: 229; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTROPHYSICS; BALLOONS; CHROMOSPHERE; ELECTRIC CURRENTS; EQUILIBRIUM; FORCE-FREE MAGNETIC FIELDS; LAYERS; LORENTZ FORCE; NOISE; PHOTOSPHERE; POLARIMETRY; SIGNAL-TO-NOISE RATIO; SPATIAL RESOLUTION; STOKES PARAMETERS; SUN

Citation Formats

Wiegelmann, T., Solanki, S. K., Barthol, P., Gandorfer, A., Gizon, L., Hirzberger, J., Riethmüller, T. L., Noort, M. van, Neukirch, T., Nickeler, D. H., Rodríguez, J. Blanco, Iniesta, J. C. Del Toro, Suárez, D. Orozco, Schmidt, W., Pillet, V. Martínez, and Knölker, M., E-mail: wiegelmann@mps.mpg.de. Magneto-static Modeling from Sunrise/IMaX: Application to an Active Region Observed with Sunrise II. United States: N. p., 2017. Web. doi:10.3847/1538-4365/AA582F.
Wiegelmann, T., Solanki, S. K., Barthol, P., Gandorfer, A., Gizon, L., Hirzberger, J., Riethmüller, T. L., Noort, M. van, Neukirch, T., Nickeler, D. H., Rodríguez, J. Blanco, Iniesta, J. C. Del Toro, Suárez, D. Orozco, Schmidt, W., Pillet, V. Martínez, & Knölker, M., E-mail: wiegelmann@mps.mpg.de. Magneto-static Modeling from Sunrise/IMaX: Application to an Active Region Observed with Sunrise II. United States. doi:10.3847/1538-4365/AA582F.
Wiegelmann, T., Solanki, S. K., Barthol, P., Gandorfer, A., Gizon, L., Hirzberger, J., Riethmüller, T. L., Noort, M. van, Neukirch, T., Nickeler, D. H., Rodríguez, J. Blanco, Iniesta, J. C. Del Toro, Suárez, D. Orozco, Schmidt, W., Pillet, V. Martínez, and Knölker, M., E-mail: wiegelmann@mps.mpg.de. Wed . "Magneto-static Modeling from Sunrise/IMaX: Application to an Active Region Observed with Sunrise II". United States. doi:10.3847/1538-4365/AA582F.
@article{osti_22661238,
title = {Magneto-static Modeling from Sunrise/IMaX: Application to an Active Region Observed with Sunrise II},
author = {Wiegelmann, T. and Solanki, S. K. and Barthol, P. and Gandorfer, A. and Gizon, L. and Hirzberger, J. and Riethmüller, T. L. and Noort, M. van and Neukirch, T. and Nickeler, D. H. and Rodríguez, J. Blanco and Iniesta, J. C. Del Toro and Suárez, D. Orozco and Schmidt, W. and Pillet, V. Martínez and Knölker, M., E-mail: wiegelmann@mps.mpg.de},
abstractNote = {Magneto-static models may overcome some of the issues facing force-free magnetic field extrapolations. So far they have seen limited use and have faced problems when applied to quiet-Sun data. Here we present a first application to an active region. We use solar vector magnetic field measurements gathered by the IMaX polarimeter during the flight of the Sunrise balloon-borne solar observatory in 2013 June as boundary conditions for a magneto-static model of the higher solar atmosphere above an active region. The IMaX data are embedded in active region vector magnetograms observed with SDO /HMI. This work continues our magneto-static extrapolation approach, which was applied earlier to a quiet-Sun region observed with Sunrise I. In an active region the signal-to-noise-ratio in the measured Stokes parameters is considerably higher than in the quiet-Sun and consequently the IMaX measurements of the horizontal photospheric magnetic field allow us to specify the free parameters of the model in a special class of linear magneto-static equilibria. The high spatial resolution of IMaX (110–130 km, pixel size 40 km) enables us to model the non-force-free layer between the photosphere and the mid-chromosphere vertically by about 50 grid points. In our approach we can incorporate some aspects of the mixed beta layer of photosphere and chromosphere, e.g., taking a finite Lorentz force into account, which was not possible with lower-resolution photospheric measurements in the past. The linear model does not, however, permit us to model intrinsic nonlinear structures like strongly localized electric currents.},
doi = {10.3847/1538-4365/AA582F},
journal = {Astrophysical Journal, Supplement Series},
number = 1,
volume = 229,
place = {United States},
year = {Wed Mar 01 00:00:00 EST 2017},
month = {Wed Mar 01 00:00:00 EST 2017}
}
  • Our aim is to model the three-dimensional magnetic field structure of the upper solar atmosphere, including regions of non-negligible plasma beta. We use high-resolution photospheric magnetic field measurements from SUNRISE/IMaX as the boundary condition for a magneto-static magnetic field model. The high resolution of IMaX allows us to resolve the interface region between the photosphere and corona, but modeling this region is challenging for the following reasons. While the coronal magnetic field is thought to be force-free (the Lorentz force vanishes), this is not the case in the mixed plasma β environment in the photosphere and lower chromosphere. In ourmore » model, pressure gradients and gravity forces are self-consistently taken into account and compensate for the non-vanishing Lorentz force. Above a certain height (about 2 Mm) the non-magnetic forces become very weak and consequently the magnetic field becomes almost force-free. Here, we apply a linear approach where the electric current density consists of a superposition of a field-line parallel current and a current perpendicular to the Sun's gravity field. We illustrate the prospects and limitations of this approach and give an outlook for an extension toward a nonlinear model.« less
  • Using the IMaX instrument on board the SUNRISE stratospheric balloon telescope, we have detected extremely shifted polarization signals around the Fe I 5250.217 A spectral line within granules in the solar photosphere. We interpret the velocities associated with these events as corresponding to supersonic and magnetic upflows. In addition, they are also related to the appearance of opposite polarities and highly inclined magnetic fields. This suggests that they are produced by the reconnection of emerging magnetic loops through granular upflows. The events occupy an average area of 0.046 arcsec{sup 2} and last for about 80 s, with larger events havingmore » longer lifetimes. These supersonic events occur at a rate of 1.3 x 10{sup -5} occurrences per second per arcsec{sup 2}.« less
  • Until today, the small size of magnetic elements in quiet-Sun areas has required the application of indirect methods, such as the line-ratio technique or multi-component inversions, to infer their physical properties. A consistent match to the observed Stokes profiles could only be obtained by introducing a magnetic filling factor that specifies the fraction of the observed pixel filled with magnetic field. Here, we investigate the properties of a small magnetic patch in the quiet Sun observed with the IMaX magnetograph on board the balloon-borne telescope SUNRISE with unprecedented spatial resolution and low instrumental stray light. We apply an inversion techniquemore » based on the numerical solution of the radiative transfer equation to retrieve the temperature stratification and the field strength in the magnetic patch. The observations can be well reproduced with a one-component, fully magnetized atmosphere with a field strength exceeding 1 kG and a significantly enhanced temperature in the mid to upper photosphere with respect to its surroundings, consistent with semi-empirical flux tube models for plage regions. We therefore conclude that, within the framework of a simple atmospheric model, the IMaX measurements resolve the observed quiet-Sun flux tube.« less
  • We report on the photospheric evolution of an intermediate-scale ( Almost-Equal-To 4 Mm footpoint separation) magnetic bipole, from emergence to decay, observed in the quiet Sun at high spatial (0.''3) and temporal (33 s) resolution. The observations were acquired by the Imaging Magnetograph Experiment imaging magnetograph during the first science flight of the SUNRISE balloon-borne solar observatory. The bipole flux content is 6 Multiplication-Sign 10{sup 17} Mx, representing a structure bridging the gap between granular scale bipoles and the smaller ephemeral regions. Footpoints separate at a speed of 3.5 km s{sup -1} and reach a maximum distance of 4.5 Mmmore » before the field dissolves. The evolution of the bipole is revealed to be very dynamic: we found a proper motion of the bipole axis and detected a change of the azimuth angle of 90 Degree-Sign in 300 s, which may indicate the presence of some writhe in the emerging structure. The overall morphology and behavior are in agreement with previous analyses of bipolar structures emerging at the granular scale, but we also found several similarities with emerging flux structures at larger scales. The flux growth rate is 2.6 Multiplication-Sign 10{sup 15} Mx s{sup -1}, while the mean decay rate is one order of magnitude smaller. We describe in some detail the decay phase of the bipole footpoints that includes break up into smaller structures, and interaction with preexisting fields leading to cancellation, but it appears to be dominated by an as-yet unidentified diffusive process that removes most of the flux with an exponential flux decay curve. The diffusion constant (8 Multiplication-Sign 10{sup 2} km{sup 2} s{sup -1}) associated with this decay is similar to the values used to describe the large-scale diffusion in flux transport models.« less
  • The evolution of the physical parameters of magnetic bright points (MBPs) located in the quiet Sun (mainly in the interwork) during their lifetime is studied. First, we concentrate on the detailed description of the magnetic field evolution of three MBPs. This reveals that individual features follow different, generally complex, and rather dynamic scenarios of evolution. Next, we apply statistical methods on roughly 200 observed MBP evolutionary tracks. MBPs are found to be formed by the strengthening of an equipartition field patch, which initially exhibits a moderate downflow. During the evolution, strong downdrafts with an average velocity of 2.4 km s{supmore » –1} set in. These flows, taken together with the concurrent strengthening of the field, suggest that we are witnessing the occurrence of convective collapses in these features, although only 30% of them reach kG field strengths. This fraction might turn out to be larger when the new 4 m class solar telescopes are operational as observations of MBPs with current state of the art instrumentation could still be suffering from resolution limitations. Finally, when the bright point disappears (although the magnetic field often continues to exist) the magnetic field strength has dropped to the equipartition level and is generally somewhat weaker than at the beginning of the MBP's evolution. Also, only relatively weak downflows are found on average at this stage of the evolution. Only 16% of the features display upflows at the time that the field weakens, or the MBP disappears. This speaks either for a very fast evolving dynamic process at the end of the lifetime, which could not be temporally resolved, or against strong upflows as the cause of the weakening of the field of these magnetic elements, as has been proposed based on simulation results. It is noteworthy that in about 10% of the cases, we observe in the vicinity of the downflows small-scale strong (exceeding 2 km s{sup –1}) intergranular upflows related spatially and temporally to these downflows. The paper is complemented by a detailed discussion of aspects regarding the applied methods, the complementary literature, and in depth analysis of parameters like magnetic field strength and velocity distributions. An important difference to magnetic elements and associated bright structures in active region plage is that most of the quiet Sun bright points display significant downflows over a large fraction of their lifetime (i.e., in more than 46% of time instances/measurements they show downflows exceeding 1 km s{sup –1}).« less