Flows and Magnetic Fields in Complex Sunspots and their Role in Producing Solar Flares

• Applicant: Professor Dr. Carsten Denker
• Subject Area: Astrophysics and Astronomy
• Term: from 2011 to 2016
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 203191995

• Final Report Year: 2016

Final Report Abstract

Solar energetic events potentially affect the Earth and the near-Earth environment. These events can also have a significant impact on technical systems oth in space and on the ground. The goal of this research project was to investigated mechanisms that trigger flares, filament/prominence eruptions, and coronal mass ejections (CMEs). The focus was on fundamental questions about the nature of flares and other eruptive events, which were studied with high-resolutions observations obtained with ground-based instruments complemented by data from various space missions. Towards the end of the research project GREGOR spectroscopic and polarimetric data became available so that the developed data pipeline was seamlessly integrated into the operation of Europe’s largest solar telescope. The initial work also aided in the definition of observing plans and instrument set-ups. Scientific results of the project “Flows and Magnetic Fields in Complex Sunspots and their Role in Producing Solar Flares” can e summarized as: – Even quiet-Sun filaments are prone to erupt once newly emerging flux destabilizes the the magnetic field topology of the filament channel or if strong shear flows develop over time. Recurrent CMEs and refilling the filament channel with cool plasma were observed in an exceptionally large filament indicating that these processes happen on all spatial scales. – Shear flows along the magnetic neutral line potentially contribute to the build-up of magnetic shear enhancing the free energy, which can be releases in flares. This effect should be especially strong in δ-spots, where opposite magnetic polarities exist in the same penumbra leading to strong magnetic field gradients. However, shear-flows can also release magnetic tension so that not all δ-spots produce energetic events. – Peculiar flows and intertwined magnetic flux systems along with flux emergence can lead to major flares. The leading sunspot of an active region suddenly splits into two parts, which rapidly separate whereby one sunspot exhibited significant rotation. This is clear evidence for strong twist of magnetic flux in subsurface layers, when flux tubes rise from the tachocline through the convection zone to the photosphere. – The penumbra of sunspots is still not well understood because of the intricate interaction of plasma flows with magnetic field lines. This leads to flux tubes with different inclination angles, where the more horizontal one carry the outward-directed Evershed flow and the associated moat flow. The latter is linked to moving magnetic features, which are likely responsible for eroding the sunspots magnetic field in its decay phase.

Publications

• 2013, Formation of a Penumbra in a Decaying Sunspot, Astronomy and Astrophysics 552, L7
  Louis, R. E., Mathew, S. K., Puschmann, K. G., Beck, C., and Balthasar, H.
  
• 2014, Near-Infrared Spectropolarimetry of a δ-Spot, Astronomy and Astrophysics 562, L6
  Balthasar, H., Beck, C., Louis, R. E., Verma, M., Denker, C.
  
• 2014, Sunspot Splitting Triggering an Eruptive Flare, Astronomy and Astrophysics 562, A110
  Louis, R. E., Puschmann, K. G., Kliem, B., Balthasar, H., Denker, C.
  
• 2015, Triggering an Eruptive Flare by Emerging Flux in a Solar Active-Region Complex, Solar Physics 290, 3641
  Louis, R. E., Kliem, B., Ravindra, B., Chintzoglou, G.
  
• 2016, Horizontal Flow Fields in and around a Small Active region. The Transition Period between Flux Emergence and Decay. Astronomy and Astrophysics 596, A3
  Verma, M., Denker, C., Balthasar, H., Kuckein, C., Gonzlez Manrique, S. J., Sobotka, M., Bello Gonzlez, N., Hoch, S., Diercke, A., Kummerow, P., Berkefeld, T., Collados, M., Feller, A., Hofmann, A., Kneer, F., Lagg, A., Lhner-Bttcher, J., Nicklas, H., Pastor Yabar, A., Schlichenmaier, R., Schmidt, D., Schmidt, W., Schubert, M., Sigwarth, M., Solanki, S. K., Soltau, D., Staude, J., Strassmeier, K. G., Volkmer, R., von der Lhe, O., Waldmann, T.
  
• 2016, Slipping Reconnection in a Solar Flare Observed in High Resolution with the GREGOR Solar Telescope, Astronomy & Astrophysics 596, A1
  Sobotka, M., Dudik J., Denker, C., Balthasar, H., Jurčák, J., Liu, W., Berkefeld, T., Collados Vera, M., Feller, A., Hofmann, A., Kneer, F., Kuckein, C., Lagg, A., Louis, R. E., von der Lühe, O., Nicklas, H., Schlichenmaier, R., Schmidt, D., Schmidt, W., Sigwarth, M., Solanki, S. K., Soltau, D., Staude, J., Strassmeier, K. G., Volkmer, R., Waldmann, T.