Main Objective: Investigate the evolution of electric currents in the chromosphere from the NLFFF modeling and He I 10830Å;
Scientific Justification: Sheared or twisted magnetic fields containing free energy play an important role in the explosive phenomena, i.e., solar flares and CMEs (coronal mass ejections). The free energy is thought to be stored by the emergence of the twisted magnetic field or the photospheric shear/rotation motion. Such photospheric motions may generate free energy as electric current density and transport to the chromosphere and the corona. It is important to know the electric current distribution to understand the energy storage process in the active region.
NLFFF (Nonlinear force-free field) modeling is currently a strong tool for getting insights of the magnetic structure in the corona. Schrijver et al. (2008) studied the three-dimensional electric currents distribution both before and after flares by the NLFFF modeling based on Hinode data. They found that the electric currents decreased after the solar flare occurred. However, there is
one critical problem for the NLFFF modeling. The photospheric magnetic field, which is usually used as boundary condition for NLFFF calculation, does not satisfy the force-free condition (Gray 2001). So the electric currents derived from the NLFFF modeling have also some uncertainties.
Our aim is to investigate the deviation between the electric currents in the chromosphere from the NLFFF modeling from SOT/SP data and that from the He I 10830 Å obtained by GREGOR/GRIS. In other words, we will focus on the non-force-freeness in the layer between the photosphere and the chromosphere above the sunspot.
Obtaining the vector magnetic field map in the chromosphere from Stokes IQUV in He I 10830Å is challenging. Some previous studies (Sasso et al. 2006; Yelles et al. 2012) have adopted Milne-Eddington atmosphere to invert the He I 10830Å. We are now trying to invert the data by the constant slab model with considering the atomic polarization by using HAZEL (Asensio Ramos et al. 2008). The results of HAZEL showed quite different magnetic field compared with that without considering atomic polarization. Schad et al. (2015) pointed out that it is important to consider the symmetry breaking of the radiation field and suggested that while Milne-Eddington atmosphere will provide better results in the umbra, we should consider the atomic polarization in the penumbra and outside the sunspot. We are thinking to adopt their method, which combined Milne-Eddington inversion and HAZEL. After obtaining the vector magnetic field map, we will derive the current density distribution and compare with the NLFFF modeling based on the Hinode SOT/SP data.
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