Study time series of solar active regions with sequences of magneto-hydro-static equilibria

In our group we have a long experience of studying sequences of stationary equilibria of the solar corona above active regions with force-free models. While the solar corona contains a low plasma-beta (ratio of plasma pressure and magnetic pressure) and can be modelled under the assumption of a vanishing Lorentz force, this is not the case at lower altitudes, in the photosphere and chromosphere. As seen in the figure, the plasma-beta may vary over several orders of magnitudes here. Consequently these lower layers of the solar atmosphere are challenging to model, because magnetic and plasma forces have to be taken self-consistently into account, which can be done by the magneto-hydro-static (MHS) code developed in our group. Until now the MHS-model has been applied to single snapshots at times when observations have been made with Sunrise/IMaX (June 2009 and June 2013). Within this project we aim to study the evolution of magnetic fields and plasma in the photosphere, chromosphere and their connection to the corona. As boundary condition the code will use time series of photospheric vector magnetograms. Output of the code are 3D-models of magnetic field, plasma pressure and density and electric currents. A sophisticated analysis of the model allows to study the temporal evolution of the magnetic energy and helicity and their association to eruptive phenomena. Furthermore the models will help to guide the analysis of images and spectra observed with Hinode/EIS, IRIS and Gregor. Key questions are:

  • How are energy and matter supplied from the lower solar atmosphere into the corona?
  • At which heights does the solar atmosphere become force-free? And how the Lorentz force affects the magnetic structure?
  • How do chromospheric magnetic field measurements compare with the MHS-model?
  • Which role have field-aligned and transverse currents?

Further reading:

Julia Katharina Thalmann, Evolution of coronal magnetic fields, PhD Thesis, Technische Universität Braunschweig, 2010.
T. Wiegelmann, T. Neukirch, D. H. Nickeler, S. K. Solanki, P. Barthol, A. Gandorfer, L. Gizon, J. Hirzberger, T. L. Riethmüller, M. van Noort, J. Blanco Rodríguez, J. C. Del Toro Iniesta, D. Orozco Suárez, W. Schmidt, V. Martínez Pillet, and M. Knölker, "Magneto-static Modeling from Sunrise/IMaX: Application to an Active Region Observed with Sunrise II," Astrophysical Journal, Suppl. Ser. 229, 18 (2017).
X. Zhu and Thomas Wiegelmann, "Testing magnetohydrostatic extrapolation with radiative MHD simulation of a solar flare," Astronomy and Astrophysics 631, A162 (2019).

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