Inclinations of small quiet-Sun magnetic features based on a new geometric approach

Jafarzadeh, S.,Solanki, S. K.,Lagg, A.,Bellot Rubio, L. R.,van Noort, M.,Feller, A.,Danilovic, S. Springer-Verlag 2014 Astronomy and astrophysics Vol.569 No.-

THE FORMATION AND DISINTEGRATION OF MAGNETIC BRIGHT POINTS OBSERVED BY<i>SUNRISE</i>/IMaX

Utz, D.,del Toro Iniesta, J. C.,Bellot Rubio, L. R.,Jurč,á,k, J.,Martí,nez Pillet, V.,Solanki, S. K.,Schmidt, W. IOP Publishing 2014 The Astrophysical journal Vol.796 No.2

<P>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(-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 4mclass 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-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(-1)).</P>

Convectively Driven Sinks and Magnetic Fields in the Quiet-Sun

Requerey, Iker S.,Del Toro Iniesta, Jose Carlos,Rubio, Luis R. Bellot,Pillet, Valentí,n Martí,nez,Solanki, Sami K.,Schmidt, Wolfgang American Astronomical Society 2017 The Astrophysical journal Supplement series Vol.229 No.1

<P>We study the relation between mesogranular flows, convectively driven sinks and magnetic fields using high spatial resolution spectropolarimetric data acquired with the Imaging Magnetograph eXperiment on board SUNRISE. We obtain the horizontal velocity flow fields of two quiet-Sun regions (31.2 x 31.2 Mm(2)) via local correlation tracking. Mesogranular lanes and the central position of sinks are identified using Lagrange tracers. We find 6.7 x 10(-2) sinks per Mm(2) in the two observed regions. The sinks are located at the mesogranular vertices and turn out to be associated with (1) horizontal velocity flows converging to a central point and (2) long-lived downdrafts. The spatial distribution of magnetic fields in the quiet-Sun is also examined. The strongest magnetic fields are preferentially located at sinks. We find that 40% of the pixels with longitudinal components of the magnetic field stronger than 500 G are located in the close neighborhood of sinks. In contrast, the small-scale magnetic loops detected by Martinez Gonzalez et al. in the same two observed areas do not show any preferential distribution at mesogranular scales. The study of individual examples reveals that sinks can play an important role in the evolution of quiet-Sun magnetic features.</P>

THE FRONTIER BETWEEN SMALL-SCALE BIPOLES AND EPHEMERAL REGIONS IN THE SOLAR PHOTOSPHERE: EMERGENCE AND DECAY OF AN INTERMEDIATE-SCALE BIPOLE OBSERVED WITH SUNRISE/IMaX

Guglielmino, S. L.,Martí,nez Pillet, V.,Bonet, J. A.,del Toro Iniesta, J. Carlos,Bellot Rubio, L. R.,Solanki, S. K.,Schmidt, W.,Gandorfer, A.,Barthol, P.,Knö,lker, M. IOP Publishing 2012 The Astrophysical journal Vol.745 No.2

<P>We report on the photospheric evolution of an intermediate-scale (approximate 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 6x10(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(-1) and reach a maximum distance of 4.5 Mm 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 degrees 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 x 10(15) Mx s(-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 x 10(2) km(2) s(-1)) associated with this decay is similar to the values used to describe the large-scale diffusion in flux transport models.</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

Magnetic field emergence in mesogranular-sized exploding granules observed with sunrise/IMaX data

Palacios, J.,Blanco Rodrí,guez, J.,Vargas Domí,nguez, S.,Domingo, V.,Martí,nez Pillet, V.,Bonet, J. A.,Bellot Rubio, L. R.,Iniesta, J. C. del Toro,Solanki, S. K.,Barthol, P.,Gandorfe EDP Sciences 2012 Astronomy and astrophysics Vol.537 No.-

<P>We report on magnetic field emergences covering significant areas of exploding granules. The balloon-borne mission SUNRISE provided high spatial and temporal resolution images of the solar photosphere. Continuum images, longitudinal and transverse magnetic field maps and Dopplergrams obtained by IMaX onboard SUNRISE are analyzed by local correlation traking (LCT), divergence calculation and time slices, Stokes inversions and numerical simulations are also employed. We characterize two mesogranular-scale exploding granules where~10<SUP>18</SUP> Mx of magnetic flux emerges. The emergence of weak unipolar longitudinal fields (~100 G) start with a single visible magnetic polarity, occupying their respective granules’ top and following the granular splitting. After a while, mixed polarities start appearing, concentrated in downflow lanes. The events last around 20 min. LCT analyses confirm mesogranular scale expansion, displaying a similar pattern for all the physical properties, and divergence centers match between all of them. We found a similar behaviour with the emergence events in a numerical MHD simulation. Granule expansion velocities are around 1 kms<SUP>−1</SUP> while magnetic patches expand at 0.65 kms<SUP>−1</SUP>. One of the analyzed events evidences the emergence of a loop-like structure. Advection of the emerging magnetic flux features is dominated by convective motion resulting from the exploding granule due to the magnetic field frozen in the granular plasma. Intensification of the magnetic field occurs in the intergranular lanes, probably because of being directed by the downflowing plasma.</P>