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Solar Coronal Loops Associated with Small-scale Mixed Polarity Surface Magnetic Fields
Chitta, L. P.,Peter, 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,Suá,rez, D. Or American Astronomical Society 2017 The Astrophysical journal, Supplement series Vol.229 No.1
<P>How and where are coronal loops rooted in the solar lower atmosphere? The details of the magnetic environment and its evolution at the footpoints of coronal loops are crucial to understanding the processes of mass and energy supply to the solar corona. To address the above question, we use high-resolution line-of-sight magnetic field data from the Imaging Magnetograph eXperiment instrument on the SUNRISE balloon-borne observatory and coronal observations from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory of an emerging active region. We find that the coronal loops are often rooted at the locations with minor small-scale but persistent opposite-polarity magnetic elements very close to the larger dominant polarity. These opposite-polarity small-scale elements continually interact with the dominant polarity underlying the coronal loop through flux cancellation. At these locations we detect small inverse Y-shaped jets in chromospheric Ca II H images obtained from the SUNRISE Filter Imager during the flux cancellation. Our results indicate that magnetic flux cancellation and reconnection at the base of coronal loops due to mixed polarity fields might be a crucial feature for the supply of mass and energy into the corona.</P>
Danilovic, S.,Solanki, S. K.,Barthol, P.,Gandorfer, A.,Gizon, L.,Hirzberger, J.,Riethmü,ller, T. L.,van Noort, M.,Rodrí,guez, J. Blanco,Del Toro Iniesta, J. C.,Suá,rez, D. Orozco,Schmi American Astronomical Society 2017 The Astrophysical journal, Supplement series Vol.229 No.1
<P>Ellerman Bombs are signatures of magnetic reconnection, which is an important physical process in the solar atmosphere. How and where they occur is a subject of debate. In this paper, we analyze SUNRISE/IMaX data, along with 3D MHD simulations that aim to reproduce the exact scenario proposed for the formation of these features. Although the observed event seems to be more dynamic and violent than the simulated one, simulations clearly confirm the basic scenario for the production of EBs. The simulations also reveal the full complexity of the underlying process. The simulated observations show that the Fe I 525.02 nm line gives no information on the height where reconnection takes place. It can only give clues about the heating in the aftermath of the reconnection. However, the information on the magnetic field vector and velocity at this spatial resolution is extremely valuable because it shows what numerical models miss and how they can be improved.</P>
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>
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>
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>
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>
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>
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>
Transverse Oscillations in Slender Ca ii H Fibrils Observed with Sunrise/SuFI
Jafarzadeh, S.,Solanki, S. K.,Gafeira, R.,Noort, M. van,Barthol, P.,Rodrí,guez, J. Blanco,Iniesta, J. C. del Toro,Gandorfer, A.,Gizon, L.,Hirzberger, J.,Knö,lker, M.,Suá,rez, D. Orozco American Astronomical Society 2017 The Astrophysical journal, Supplement series Vol.229 No.1
<P>We present observations of transverse oscillations in slender Ca II H fibrils (SCFs) in the lower solar chromosphere. We use a 1 hr long time series of high- (spatial and temporal-) resolution. seeing-free observations in a 1.1 angstrom wide passband covering the line core of Ca II H 3969 angstrom from the second flight of the SUNRISE balloon-borne solar observatory. The entire field of view, spanning the polarity inversion line of an active region close to the solar disk center, is covered with bright, thin, and very dynamic fine structures. Our analysis reveals the prevalence of transverse waves in SCFs with median amplitudes and periods on the order of 2.4 +/- 0.8 km s(-1) and 83 +/- 29 s, respectively (with standard deviations given as uncertainties). We find that the transverse waves often propagate along (parts of) the SCFs with median phase speeds of 9 +/- 14 km s(-1). While the propagation is only in one direction along the axis in some of the SCFs, propagating waves in both directions, as well as standing waves are also observed. The transverse oscillations are likely Alfvenic and are thought to be representative of magnetohydrodynamic kink waves. The wave propagation suggests that the rapid. high-frequency transverse waves,. often produced in the lower photosphere, can penetrate into the chromosphere. with an estimated energy flux of approximate to 15 kW m(-2). Characteristics of these waves differ from those reported for other fibrillar structures, which, however, were observed mainly in the upper solar chromosphere.</P>