Document Type

Dissertation

Date of Award

12-31-2020

Degree Name

Doctor of Philosophy in Applied Physics - (Ph.D.)

Department

Physics

First Advisor

Haimin Wang

Second Advisor

Chang Liu

Third Advisor

Dale E. Gary

Fourth Advisor

Wenda Cao

Fifth Advisor

Chengjun Liu

Abstract

The evolution of photospheric magnetic fields is considered as the fundamental source of forming atmospheric structures and triggering most solar activities, including flares and mass ejections on various scales (CMEs, jets, etc.). With the implementation of high-resolution observational instruments, small-scale details of magnetic features are recognized that can provide important information regarding the evolution in active regions and the connection between photospheric magnetic reconnection and jet-like ejections in the quiet Sun. This research takes advantage of the exceptionally high-resolution measurements of vector magnetic field and imaging observations by the Goode Solar Telescope, and UV/EUV imaging observations from space-based instruments. The studied topics include structural evolution of penumbra and shear flows in response to a flare eruption, flux emergence in the formation of an active region, and small-scale magnetic reconnections in the photosphere in a coronal boundary. The main findings in this dissertation work are listed as follows:

  • Using high-resolution imaging observation in the TiO band by GST and photospheric vector magnetic field observation by the Helioseismic and Magnetic Imager, strong shear flow expansion in a precursor kernel near the polarity inversion line (PIL) is found to be closely associated with the M6.5 flare in AR 12371, which indicates a linkage between small-scale magnetic changes and the flare eruption. The flow field of the penumbra in the flaring core region is calculated using the differential affine velocity estimator. An enhancement of penumbral flows and an extension of penumbral fibrils after the first peak of the flare hard X-ray (HXR) emission are observed to be accompanied by a rapid increase of the horizontal field. These results provide evidence of the back reaction theory of coronal restructuring on the photosphere as a result of flare energy release.
  • Taking advantage of high-resolution magnetic field measurements, TiO continuum, and H-alpha observations by GST, small-scale magnetic flux emergences in the AR 12665 are observed in two types of topology: magnetic flux sheet emergence associated with the newly forming granules, and the traditional magnetic flux loop emergence. Both types of flux emergence are associated with the darkening of granular boundaries, while only flux sheets elongate granules along the direction of emerging magnetic fields and expand laterally. H-alpha observations reveal transient brightenings in the events of magnetic loop emergence, which are most probably the signatures of Ellerman bombs.
  • Statistical study of small-scale magnetic reconnections around the coronal hole boundary is achieved by tracking magnetic features with the Southwest Automatic Magnetic Identification Suite (SWAMIS). The tracking results show that the magnetic energy release rate by small-scale cancellation inside the coronal hole is 3 times higher than that outside the coronal hole. Spicules are likely associated with these kinds of reconnections, while only a small portion of the release magnetic energy is directly deposited to hot plasma.

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