September 21, 2012, 12:00 pm - 1:00 pm
September 21, 12:00 pm - 1:00 pm
Nonlinear force-free reconstruction of the coronal magnetic field with advanced numerical methods in spherical geometry
Dr. Tilaye Tadesse, Dept of Physics, Drexel University
It is commonly believed that the magnetic field plays an important role in active solar phenomena: solar flares, coronal mass ejections, and other solar eruptive activities. The knowledge of three-dimensional (3D) magnetic-field properties is essential for our understanding of the physical mechanism of these activities. Unfortunately, the direct measurement of the 3D magnetic field in higher solar atmospheres is far less precise and sophisticated than in the photosphere. The currently most common and accurate way of overcoming this is to extrapolate the magnetic field into the solar chromosphere and corona, based on an assumed model and using the observed photospheric magnetic field as a boundary condition. There have been several techniques developed for the extrapolation of the magnetic field for this purpose. In test of nonlinear force-free codes by SDO/HMI data analysis team our Cartesian code as implemented by Wiegelmann (2004) was the fastest converging and the best performing one for analytical test cases and it is being selected to be part of SDO/HMI data product pipeline. In general, extrapolation codes in cartesian geometry do not take the curvature of the Sun’s surface into account and can only be applied to relatively small areas, e.g., a single active region. Large model volumes at high spatial resolution are required to accommodate the magnetic connectivity within an active region and the surrounding environment. This requirement can only be met if the computational box for the field extrapolation is enhanced beyond a size where the solar spherical geometry can be neglected. In this presentation, I will show optimization method used for reconstruction of nonlinear force-free coronal magnetic fields in spherical geometry in a larger FOV from SDO/HMI and SOLIS data sets. These NLFFF tools help us to study the quasi-static equilibrium of sequences of magnetograms from SDO/HMI and other ground based telescopes to monitor the change of the coronal magnetic field configuration which is a potential indicator for forecasting flare and CME eruptions.