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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>
Observations of solar chromospheric heating at sub-arcsec spatial resolution
Smitha, H. N.,Chitta, L. P.,Wiegelmann, T.,Solanki, S. K. Springer-Verlag 2018 Astronomy and astrophysics Vol.617 No.-
<P>A wide variety of phenomena such as gentle but persistent brightening, dynamic slender features (∼100 km), and compact (∼1″) ultraviolet (UV) bursts are associated with the heating of the solar chromosphere. High spatio-temporal resolution is required to capture the finer details of the likely magnetic reconnection-driven, rapidly evolving bursts. Such observations are also needed to reveal their similarities to large-scale flares, which are also thought to be reconnection driven, and more generally their role in chromospheric heating. Here we report observations of chromospheric heating in the form of a UV burst obtained with the balloon-borne observatory SUNRISE. The observed burst displayed a spatial morphology similar to that of a large-scale solar flare with a circular ribbon. While the co-temporal UV observations at 1.5″ spatial resolution and 24 s cadence from the Solar Dynamics Observatory showed a compact brightening, the SUNRISE observations at diffraction-limited spatial resolution of 0.1″ at 7 s cadence revealed a dynamic substructure of the burst that it is composed of an extended ribbon-like feature and a rapidly evolving arcade of thin (∼0.1″) magnetic loop-like features, similar to post-flare loops. Such a dynamic substructure reveals the small-scale nature of chromospheric heating in these bursts. Furthermore, based on magnetic field extrapolations, this heating event is associated with a complex fan-spine magnetic topology. Our observations strongly hint at a unified picture of magnetic heating in the solar atmosphere from some large-scale flares to small-scale bursts, all associated with such a magnetic topology.</P>
Liu, Chang,Deng, Na,Lee, Jeongwoo,Wiegelmann, Thomas,Jiang, Chaowei,Dennis, Brian R.,Su, Yang,Donea, Alina,Wang, Haimin IOP Publishing 2014 The Astrophysical journal Vol.795 No.2
<P>We carry out a comprehensive investigation comparing the three-dimensional magnetic field restructuring, flare energy release, and the helioseismic response of two homologous flares, the 2011 September 6 X2.1 (FL1) and September 7 X1.8 (FL2) flares in NOAA AR 11283. In our analysis, (1) a twisted flux rope (FR) collapses onto the surface at a speed of 1.5 km s(-1) after a partial eruption in FL1. The FR then gradually grows to reach a higher altitude and collapses again at 3 km s(-1) after a fuller eruption in FL2. Also, FL2 shows a larger decrease of the flux-weighted centroid separation of opposite magnetic polarities and a greater change of the horizontal field on the surface. These imply a more violent coronal implosion with corresponding more intense surface signatures in FL2. (2) The FR is inclined northward and together with the ambient fields, it undergoes a southward turning after both events. This agrees with the asymmetric decay of the penumbra observed in the peripheral regions. (3) The amounts of free magnetic energy and nonthermal electron energy released during FL1 are comparable to those of FL2 within the uncertainties of the measurements. (4) No sunquake was detected in FL1; in contrast, FL2 produced two seismic emission sources S1 and S2 both lying in the penumbral regions. Interestingly, S1 and S2 are connected by magnetic loops, and the stronger source S2 has a weaker vertical magnetic field. We discuss these results in relation to the implosion process in the low corona and the sunquake generation.</P>
MESOGRANULATION AND THE SOLAR SURFACE MAGNETIC FIELD DISTRIBUTION
Yelles Chaouche, L.,Moreno-Insertis, F.,Martí,nez Pillet, V.,Wiegelmann, T.,Bonet, J. A.,Knö,lker, M.,Bellot Rubio, L. R.,del Toro Iniesta, J. C.,Barthol, P.,Gandorfer, A.,Schmidt, W.,Solank IOP Publishing 2011 ASTROPHYSICAL JOURNAL LETTERS - Vol.727 No.2
EVOLUTION OF RELATIVE MAGNETIC HELICITY AND CURRENT HELICITY IN NOAA ACTIVE REGION 11158
Jing, Ju,Park, Sung-Hong,Liu, Chang,Lee, Jeongwoo,Wiegelmann, Thomas,Xu, Yan,Deng, Na,Wang, Haimin IOP Publishing 2012 ASTROPHYSICAL JOURNAL LETTERS - Vol.752 No.1
<P>Both magnetic and current helicities are crucial ingredients for describing the complexity of active-region magnetic structure. In this Letter, we present the temporal evolution of these helicities contained in NOAA active region 11158 during five days from 2011 February 12 to 16. The photospheric vector magnetograms of the Helioseismic and Magnetic Imager on board the Solar Dynamic Observatory were used as the boundary conditions for the coronal field extrapolation under the assumption of nonlinear force-free field, from which we calculated both relative magnetic helicity and current helicity. We construct a time-altitude diagram in which altitude distribution of the magnitude of current helicity density is displayed as a function of time. This diagram clearly shows a pattern of upwardly propagating current helicity density over two days prior to the X2.2 flare on February 15 with an average propagation speed of similar to 36 m s(-1). The propagation is synchronous with the emergence of magnetic flux into the photosphere, and indicative of a gradual energy buildup for the X2.2 flare. The time profile of the relative magnetic helicity shows a monotonically increasing trend most of the time, but a pattern of increasing and decreasing magnetic helicity above the monotonic variation appears prior to each of two major flares, M6.6 and X2.2, respectively. The physics underlying this bump pattern is not fully understood. However, the fact that this pattern is apparent in the magnetic helicity evolution but not in the magnetic flux evolution makes it a useful indicator in forecasting major flares.</P>
Slender Ca ii H Fibrils Mapping Magnetic Fields in the Low Solar Chromosphere
Jafarzadeh, S.,Rutten, R. J.,Solanki, S. K.,Wiegelmann, T.,Riethmü,ller, T. L.,Noort, M. van,Szydlarski, M.,Rodrí,guez, J. Blanco,Barthol, P.,Iniesta, J. C. del Toro,Gandorfer, A.,Gizon, L. American Astronomical Society 2017 The Astrophysical journal, Supplement series Vol.229 No.1
<P>A dense forest of slender bright fibrils near a small solar active region is seen in high-quality narrowband Ca II H images from the SuFI instrument onboard the SUNRISE balloon-borne solar observatory. The orientation of these slender Ca II H fibrils (SCF) overlaps with the magnetic field configuration in the low solar chromosphere derived by magnetostatic extrapolation of the photospheric field observed with SUNRISE/IMaX and SDO/HMI. In addition, many observed SCFs are qualitatively aligned with small-scale loops computed from a novel inversion approach based on best-fit numerical MHD simulation. Such loops are organized in canopy-like arches over quiet areas that differ in height depending on the field strength near their roots.</P>