Stereoscopic coronal magnetic field modeling

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In the project 'Stereoscopic coronal magnetic field modeling', we want to study magnetic fields in solar active regions. Since continuous and accurate measurements of coronal magnetic field are not available, two complementary approaches have been developed to obtain the 3D structure of coronal magnetic fields: stereoscopy and extrapolation of photospheric field measurements.The accuracy of both methods is constrained by the available observational data, e.g., the ability to identify corresponding loop structures in EUV-images from different vantage points, the angle between the observing spacecraft and measurement errors in photospheric vector magnetograms. We therefore developed a new model, called 'Stereoscopic-NonLinear Force-Free Field model (S-NLFFF)' where NLFFF extrapolations from photospheric data are constrained by coronal observations. The newly developed S-NLFFF code was successfully tested with synthetic data.Within the proposed project we plan to apply this new approach to observations from SDO and STEREO in order to derive the 3D coronal magnetic field structure with unprecedented high accuracy. In a later step we will generalize our model to use EUV-images from one vantage point (SDO) only. The corresponding code can be applied to all datasets after the launch of SDO in 2010. The implementation of the S-NLFFF will be made in both Cartesian and spherical coordinates for active regions and global models, respectively.Our NLFFF-optimization code allows naturally to constrain the model by additional observations, e.g., chromospheric vector magnetograms. It will be the first time that a NLFFF method will use vector data from two different layers, photosphere, respectively chromosphere and be constrained from observations in the corona.NLFFF models are strictly valid only in the active region solar corona, but not in the photosphere and the lower part of the chromosphere. For a meaningful modeling of these layers, the plasma pressure gradient and the gravity force have to be taken into account. A corresponding self-consistent magneto-hydro-static model was developed by our group. The projections of the reconstructed 3D magnetic field lines onto multi-wavelength coronal images can be used to specify the temperature, density and pressure along coronal loops. The self-consistent magneto-hydro-static approach then models these quantities in the entire computational domain.