Computing the global coronal magnetic field during activity maximum and minimum with a newly developed nonlinear force-free Yin-Yang code

As the coronal dynamics is dominated by magnetic forces, the reconstruction of the coronal magnetic field is of major importance when studying the solar corona. Since coronal field measurements are not routinely available, photospheric fields are extrapolated into the corona in order to obtain the 3D coronal magnetic field structure. A nonlinear force-free field approximation is justified because of the low plasma  $\beta$. Previous extrapolation codes excluded high and low latitudes, because of the well know grid convergence problems at the poles. To overcome these limitations, we developed a new code implemented on a Yin-Yang grid, which was tested and verified with the Low and Lou solution as reference. Here we apply our code to synoptic vector magnetograms obtained from SDO/HMI during solar activity maximum and minimum, respectively. We compare our magnetic field models with EUV-observations of the solar corona as a first validation step.