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

¹ Image Processing Laboratory, University of Valencia, PO Box 22085, 46980 Paterna, Valencia Spain
e-mail: judith.palacios@uv.es
² Departamento de Física, Universidad de Los Andes, A.A. 4976 Bogotá, Colombia
³ Instituto de Astrofísica de Canarias, 38205 La Laguna, Tenerife, Spain
⁴ Instituto de Astrofísica de Andalucía, Apdo. de Correos 3004, 18080 Granada, Spain
⁵ Max Planck Institut für Sonnensystemforschung, Max Planck Strasse 2, 37191 Katlenburg-Lindau, Germany
⁶ Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, 79104 Freiburg, Germany
⁷ High Altitude Observatory, National Center for Atmospheric Research, PO Box 3000, Boulder, CO 80307-3000, USA
⁸ School of Space Research, Kyung Hee University, Yongin, 446-701 Gyeonggi, Republic of Korea

Received: 23 August 2011
Accepted: 18 October 2011

Abstract

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  ~10¹⁸ 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^-1 while magnetic patches expand at 0.65 kms^-1. 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.