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A New MHD-assisted Stokes Inversion Technique
Riethmü,ller, T. L.,Solanki, S. K.,Barthol, P.,Gandorfer, A.,Gizon, L.,Hirzberger, J.,Noort, M. van,Rodrí,guez, J. Blanco,Iniesta, J. C. Del Toro,Suá,rez, D. Orozco,Schmidt, W.,Pillet, American Astronomical Society 2017 The Astrophysical journal Supplement series Vol.229 No.1
<P>We present a new method of Stokes inversion of spectropolarimetric data and evaluate it by taking the example of a SUNRISE/IMaX observation. An archive of synthetic Stokes profiles is obtained by the spectral synthesis of stateof- the-art magnetohydrodynamics (MHD) simulations and a realistic degradation to the level of the observed data. The definition of a merit function allows the archive to be searched for the synthetic Stokes profiles that best match the observed profiles. In contrast to traditional Stokes inversion codes, which solve the Unno-Rachkovsky equations for the polarized radiative transfer numerically and fit the Stokes profiles iteratively, the new technique provides the full set of atmospheric parameters. This gives us the ability to start an MHD simulation that takes the inversion result as an initial condition. After a relaxation process of half an hour solar time we obtain physically consistent MHD data sets with a target similar to the observation. The new MHD simulation is used to repeat the method in a second iteration, which further improves the match between observation and simulation, resulting in a factor of 2.2 lower mean chi(2) value. One advantage of the new technique is that it provides the physical parameters on a geometrical height scale. It constitutes a first step toward inversions that give results consistent with the MHD equations.</P>
A Tale of Two Emergences: Sunrise II Observations of Emergence Sites in a Solar Active Region
Centeno, R.,Rodrí,guez, J. Blanco,Del Toro Iniesta, J. C.,Solanki, S. K.,Barthol, P.,Gandorfer, A.,Gizon, L.,Hirzberger, J.,Riethmü,ller, T. L.,Noort, M. van,Suá,rez, D. Orozco,Berkefe American Astronomical Society 2017 The Astrophysical journal Supplement series Vol.229 No.1
<P>In 2013 June, the two scientific instruments on. board the second SUNRISE mission witnessed, in detail, a small-scale magnetic flux emergence event as part of the birth of an active region. The Imaging Magnetograph Experiment (IMaX) recorded two small (similar to 5 '') emerging flux patches in the polarized filtergrams of a photospheric Fe I spectral line. Meanwhile, the SUNRISE Filter Imager (SuFI) captured the highly dynamic chromospheric response to the magnetic fields pushing their way through the lower solar atmosphere. The serendipitous capture of this event offers a closer look at the inner workings of active region emergence sites. In particular, it reveals in meticulous detail how the rising magnetic fields interact with the granulation as they push through the Sun's surface, dragging photospheric plasma in their upward travel. The plasma that is burdening the rising field slides along the field lines, creating fast downflowing channels at the footpoints. The weight of this material anchors this field to the surface at semi-regular spatial intervals, shaping it in an undulatory fashion. Finally, magnetic reconnection enables the field to release itself from its photospheric anchors, allowing it to continue its voyage up to higher layers. This process releases energy that lights up the arch-filament systems and heats the surrounding chromosphere.</P>
Moving Magnetic Features Around a Pore
Kaithakkal, A. J.,Riethmü,ller, T. L.,Solanki, S. K.,Lagg, A.,Barthol, P.,Gandorfer, A.,Gizon, L.,Hirzberger, J.,vanNoort, M.,Rodrí,guez, J. Blanco,Iniesta, J. C. Del Toro,Suá,rez, D. American Astronomical Society 2017 The Astrophysical journal, Supplement series Vol.229 No.1
<P>Spectropolarimetric observations from SUNRISE/IMaX, obtained in 2013 June, are used for a statistical analysis to determine the physical properties of moving magnetic features (MMFs) observed near a pore. MMFs of the same and opposite polarity, with respect to the pore, are found to stream from its border at an average speed of 1.3 km s(-1) and 1.2 km s(-1), respectively, with mainly same-polarity MMFs found further away from the pore. MMFs of both polarities are found to harbor rather weak, inclined magnetic fields. Opposite-polarity MMFs are blueshifted, whereas same-polarity MMFs do not show any preference for up-or downflows. Most of the MMFs are found to be of sub-arcsecond size and carry a mean flux of similar to 1.2 x 10(17) Mx.</P>
The Maximum Entropy Limit of Small-scale Magnetic Field Fluctuations in the Quiet Sun
Gorobets, A. Y.,Berdyugina, S. V.,Riethmü,ller, T. L.,Rodrí,guez, J. Blanco,Solanki, S. K.,Barthol, P.,Gandorfer, A.,Gizon, L.,Hirzberger, J.,Noort, M. van,Del Toro Iniesta, J. C.,Suá American Astronomical Society 2017 The Astrophysical journal Supplement series Vol.233 No.1
<P>The observed magnetic field on the solar surface is characterized by a very complex spatial and temporal behavior. Although feature-tracking algorithms have allowed us to deepen our understanding of this behavior, subjectivity plays an important role in the identification and tracking of such features. In this paper, we continue studies of the temporal stochasticity of the magnetic field on the solar surface without relying either on the concept of magnetic features or on subjective assumptions about their identification and interaction. We propose a data analysis method to quantify fluctuations of the line-of-sight magnetic field by means of reducing the temporal field's evolution to the regular Markov process. We build a representative model of fluctuations converging to the unique stationary (equilibrium) distribution in the long time limit with maximum entropy. We obtained different rates of convergence to the equilibrium at fixed noise cutoff for two sets of data. This indicates a strong influence of the data spatial resolution and mixing-polarity fluctuations on the relaxation process. The analysis is applied to observations of magnetic fields of the relatively quiet areas around an active region carried out during the second flight of the SUNRISE/IMAX and quiet Sun areas at the disk center from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory satellite.</P>
COMPARISON BETWEEN Mg II<i>k</i>AND Ca II H IMAGES RECORDED BY SUNRISE/SuFI
Danilovic, S.,Hirzberger, J.,Riethmü,ller, T. L.,Solanki, S. K.,Barthol, P.,Berkefeld, T.,Gandorfer, A.,Gizon, L.,Knö,lker, M.,Schmidt, W.,Rodrí,guez, J. Blanco,Iniesta, J. C. Del Toro IOP Publishing 2014 The Astrophysical journal Vol.784 No.1
<P>We present a comparison of high-resolution images of the solar surface taken in the MgII k and Ca II H channels of the Filter Imager on the balloon-borne solar observatory SUNRISE. The Mg and Ca lines are sampled with 0.48 nm and 0.11 nm wide filters, respectively. The two channels show remarkable qualitative and quantitative similarities in the quiet Sun, in an active region plage and during a small flare. However, the Mg filtergrams display 1.4-1.7 times higher intensity contrast and appear more smeared and smoothed in the quiet Sun. In addition, the fibrils in a plage are wider. Although the exposure time is 100 times longer for Mg images, the evidence suggests that these differences cannot be explained only with instrumental effects or the evolution of the solar scene. The differences at least partially arise because of different line-formation heights, the stronger response of Mg k emission peaks to the higher temperatures, and the larger height range sampled by the broad Mg filter used here. This is evidently manifested during the flare when a surge in Mg evolves differently than in Ca.</P>
Spectropolarimetric Evidence for a Siphon Flow along an Emerging Magnetic Flux Tube
Requerey, Iker S.,Cobo, B. Ruiz,Iniesta, J. C. Del Toro,Suá,rez, D. Orozco,Rodrí,guez, J. Blanco,Solanki, S. K.,Barthol, P.,Gandorfer, A.,Gizon, L.,Hirzberger, J.,Riethmü,ller, T. L.,N American Astronomical Society 2017 The Astrophysical journal Supplement series Vol.229 No.1
<P>We study the dynamics and topology of an emerging magnetic flux concentration using high spatial resolution spectropolarimetric data acquired with the Imaging Magnetograph eXperiment on board the SUNRISE balloon-borne solar observatory. We obtain the full vector magnetic field and the line of sight (LOS) velocity through inversions of the Fe I line at 525.02 nm with the SPINOR code. The derived vector magnetic field is used to trace magnetic field lines. Two magnetic flux concentrations with different polarities and LOS velocities are found to be connected by a group of arch-shaped magnetic field lines. The positive polarity footpoint is weaker (1100 G) and displays an upflow, while the negative polarity footpoint is stronger (2200 G) and shows a downflow. This configuration is naturally interpreted as a siphon flow along an arched magnetic flux tube.</P>
Solanki, S. K.,Riethmü,ller, T. L.,Barthol, P.,Danilovic, S.,Deutsch, W.,Doerr, H.-P.,Feller, A.,Gandorfer, A.,Germerott, D.,Gizon, L.,Grauf, B.,Heerlein, K.,Hirzberger, J.,Kolleck, M.,Lagg, A.,Me American Astronomical Society 2017 The Astrophysical journal, Supplement series Vol.229 No.1
<P>The SUNRISE balloon-borne solar observatory, consisting of a 1 m aperture telescope that provides a stabilized image to a UV filter imager and an imaging vector polarimeter, carried out its second science flight in 2013 June. It provided observations of parts of active regions at high spatial resolution, including the first high-resolution images in the Mg II. k line. The obtained data are of very high quality, with the best UV images reaching the diffraction limit of the telescope at 3000 angstrom after Multi-Frame Blind Deconvolution reconstruction accounting for phasediversity information. Here a brief update is given of the instruments and the data reduction techniques, which includes an inversion of the polarimetric data. Mainly those aspects that evolved compared with the first flight are described. A tabular overview of the observations is given. In addition, an example time series of a part of the emerging active region NOAA AR. 11768 observed relatively close to disk center is described and discussed in some detail. The observations cover the pores in the trailing polarity of the active region, as well as the polarity inversion line where flux emergence was ongoing and a small flare-like brightening occurred in the course of the time series. The pores are found to contain magnetic field strengths ranging up to 2500 G, and while large pores are clearly darker and cooler than the quiet Sun in all layers of the photosphere, the temperature and brightness of small pores approach or even exceed those of the quiet Sun in the upper photosphere.</P>
UNNOTICED MAGNETIC FIELD OSCILLATIONS IN THE VERY QUIET SUN REVEALED BY SUNRISE/IMaX
Martí,nez Gonzá,lez, M. J.,Asensio Ramos, A.,Manso Sainz, R.,Khomenko, E.,Martí,nez Pillet, V.,Solanki, S. K.,Ló,pez Ariste, A.,Schmidt, W.,Barthol, P.,Gandorfer, A. IOP Publishing 2011 ASTROPHYSICAL JOURNAL LETTERS - Vol.730 No.2
<P>We present observational evidence for oscillations of magnetic flux density in the quiet areas of the Sun. The majority of magnetic fields on the solar surface have strengths of the order of or lower than the equipartition field (300-500 G). This results in a myriad of magnetic fields whose evolution is largely determined by the turbulent plasma motions. When granules evolve they squash the magnetic field lines together or pull them apart. Here, we report on the periodic deformation of the shapes of features in circular polarization observed at high resolution with SUNRISE. In particular, we note that the area of patches with a constant magnetic flux oscillates with time, which implies that the apparent magnetic field intensity oscillates in antiphase. The periods associated with this oscillatory pattern are compatible with the granular lifetime and change abruptly, which suggests that these oscillations might not correspond to characteristic oscillatory modes of magnetic structures, but to the forcing by granular motions. In one particular case, we find three patches around the same granule oscillating in phase, which means that the spatial coherence of these oscillations can reach 1600 km. Interestingly, the same kind of oscillatory phenomenon is also found in the upper photosphere.</P>
Oscillations on Width and Intensity of Slender Ca ii H Fibrils from Sunrise/SuFI
Gafeira, R.,Jafarzadeh, S.,Solanki, S. K.,Lagg, A.,van Noort, M.,Barthol, P.,Rodrí,guez, J. Blanco,del Toro Iniesta, J. C.,Gandorfer, A.,Gizon, L.,Hirzberger, J.,Knö,lker, M.,Suá,rez, American Astronomical Society 2017 The Astrophysical journal, Supplement series Vol.229 No.1
<P>We report the detection of oscillations in slender Ca II H fibrils (SCFs) from high-resolution observations acquired with the SUNRISE balloon-borne solar observatory. The SCFs show obvious oscillations in their intensity, but also their width. The oscillatory behaviors are investigated at several positions along the axes of the SCFs. A large majority of fibrils show signs of oscillations in intensity. Their periods and phase speeds are analyzed using a wavelet analysis. The width and intensity perturbations have overlapping distributions of the wave period. The obtained distributions have median values of the period of 32 +/- 17 s and 36 +/- 25 s, respectively. We find that the fluctuations of both parameters propagate in the SCFs with speeds of 11(-11)(+49)+ km s(-1) and 15(-15)(+34) km s(-1), respectively. Furthermore, the width and intensity oscillations have a strong tendency to be either in anti-phase. or, to a smaller extent, in phase. This suggests that the oscillations of both parameters are caused by the same wave mode and that the waves are likely propagating. Taking all the evidence together, the most likely wave mode to explain all measurements and criteria is the fast sausage mode.</P>
Magneto-static Modeling from Sunrise/IMaX: Application to an Active Region Observed with Sunrise II
Wiegelmann, T.,Neukirch, T.,Nickeler, D. H.,Solanki, S. K.,Barthol, P.,Gandorfer, A.,Gizon, L.,Hirzberger, J.,Riethmü,ller, T. L.,Noort, M. van,Rodrí,guez, J. Blanco,Iniesta, J. C. Del Toro American Astronomical Society 2017 The Astrophysical journal Supplement series Vol.229 No.1
<P>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.</P>