Date of Award
Doctor of Philosophy in Applied Physics - (Ph.D.)
Cristiano L. Dias
Almost all solar activities observed are related to the solar magnetic field, especially the topological restructuring of magnetic fields, the so-called magnetic reconnection in solar physics. They are occurring at different scales related to various phenomena, during minimum or maximum of the solar cycle, from the photosphere to the solar corona.
For small-scale activities, type II spicules which display high velocity upflows observed at the limb, have the most possible underlying driving mechanism of magnetic reconnection. A set of tools is developed for detecting small-scale solar magnetic cancellations and the disk counterpart of type II spicules (the so-called Rapid Blueshifted Excursions, RBEs), using line-of-sight photospheric magnetograms and chromospheric spectroscopic observations, respectively. These tools are further employed to analyze coordinated observation using the Interferometric BIdimensional Spectrometer at the Dunn Solar Telescope of the National Solar Observatory and Hinode. The statistical properties of magnetic cancellations and RBEs are presented and their correlation is explored using this data set.
For large-scale activities, recent high resolution extreme-ultraviolet observation from the Solar Dynamics Observatory (SDO) is able to diagnose the plasma around current sheet, the key role of magnetic reconnection during energetic solar flares. Supra-arcade downflows (SADs) have been frequently observed during the gradual phase of flares near the limb. In coronal emission lines sensitive to flaring plasma, they appear as tadpole-like dark voids against the diffuse fan-shaped “haze” above the well-defined flare arcade and flow toward the arcade. Several selected SADs from two flare events are carefully studied. Their differential emission measures (DEMs) and DEM-weighted temperatures are calculated using data obtained by the Atmospheric Imaging Assembly onboard SDO. This analysis corroborates that SADs are density depletion associated with a substantial decrease in DEM. This depression in DEM rapidly recovers in the wake of the SADs studied, generally within a few minutes, suggesting that they are discrete features. In addition, SADs in one event are found to be spatio-temporally associated with the successive formation of post-flare loops along the flare arcade.
Chen, Xin, "Magnetic reconnection in small and large scales on the sun" (2016). Dissertations. 66.