| Presentation Title: | Relation between non-thermal broadening and magnetic field inclination at the transition region. |
| Author(s): | Kyuhyoun Cho, Bart De Pontieu, and Paola Testa |
Abstract:
The non-thermal broadening of spectral lines emitted in the solar atmosphere, an additional spectral broadening component beyond thermal and instrumental broadening, remains a poorly understood phenomenon in solar spectroscopy. In particular, its manifestation in the transition region has received significant attention as it holds the potential to elucidate the underlying physical mechanisms driving the heating and dynamics the solar atmosphere in the solar atmosphere. We investigate the relation between non-thermal broadening and magnetic field inclination in the transition region. Analyzing data acquired by the Interface Region Imaging Spectrograph (IRIS), we extracted spectral parameters from the Si IV 1403 Å line in a full-disk mosaic dataset. Magnetic field inclination at the transition region was determined through non-linear force-free field extrapolation (NLFFF), based on vector magnetic field data from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). Our analysis focused on three distinct plage regions, revealing that the region's edge facing the solar disk center exhibited comparatively strong non-thermal velocities and downward flows. In addition, the NLFFF extrapolation demonstrated alignment of the magnetic field direction in this region with the line-of-sight direction, suggesting a connection between non-thermal broadening and unresolved plasma motions along magnetic fields. This finding implies that a portion of the observed non-thermal broadening may be caused by the deceleration of falling plasma along these magnetic field lines.