Date of Award
Doctor of Philosophy in Applied Physics - (Ph.D.)
Thomas Anthony Schad
Solar spectrum in the infrared (IR) contains abundant information of solar activities, however, it has not spectral lines in the solar IR spectrum provide different tools to probe the solar atmosphere in various heights. This radiation band in such relatively long wavelength includes various atom and molecule spectral lines that are generated by relatively small energy level transitions. The temperature-sensitive and highly dynamic spectral lines could reveal the energy transmission process more easily than those in the visible wavelength of solar emission. Moreover, the better magnetic sensitivities for the infrared lines resulting from their longer wavelength make them detect the solar magnetic fields more precisely. Another reason to develop the IR solar physics is for its better observation seeing conditions.
With the advances in instrumentation techniques embodied in the 1.6-meter aperture Goode Solar Telescope (GST), Big Bear Solar Observatory (BBSO) has developed a series of high spatial and temporal resolution instruments in IR. Near- InfRared Imaging spectropolarimeter (NIRIS) provides imaging spectropolarimetric data with the Fe I 15648.5 Å and imaging spectroscopic data for the He I 10830 Å, which offer powerful tool to detect the vector magnetic field in the deepest solar photosphere and the dynamic measurement from the high chromosphere to the low transition region, respectively. CrYogenic infRAred spectrograph (CYRA) is a new facility instrument that operates at the Near-IR wavelengths in 1-5 µm, which is not only powerful for photospheric magnetic measurement but also uniquefor chromospheric structure diagnostic.
The main achievements in this dissertation are as follows: (1) The high-resolution spectroscopic imaging in He I 10830 Å and Ha for a set of active region magnetic loops of different sizes I carried out. Movies made of blue and red wing images give counter-streaming motions, i.e., chromospheric absorption features in blue and red wing images move in opposite directions, at different strands. The moving pattern is detected with the local correlation tracking method and confirmed by Doppler shifts. For counter-streaming motions in long loops, I show that unidirectional mass flows in two opposite directions are accompanied by simultaneous weak EUV brightenings. (2) Observations with the GST, showing that the emergence of new magnetic flux occurred at the edge of a filamentary light bridge I presented. The emergence was accompanied by brightness enhancement of a photospheric overturning convection cell at the endpoints of the emerging magnetic structure. A fan-shaped jet was observed to be spatially and temporally correlated with the endpoint of the OCC intruding into the light bridge. My observation is the first report of flux emergence within a granular light bridge with evidence in the evolution of vector magnetic field as well as photosphere convection motions and supports the idea that the impulsive jets above the light bridge are caused by magnetic reconnection. (3) CYRA is the first fully cryogenic spectrograph in any solar observatory. It has been installed and the author is involved in the implementation, commission as well as the data acquisition and reduction for CYRA. The preliminary scientific results have been highlighted as well in this dissertation.
Yang, Xu, "Investigation of small-scale energy release and transfer processes in the solar atmosphere with high-resolution observations in infrared" (2019). Dissertations. 1438.