Abstract Details

Name: Upendra Kumar Singh Kushwaha
Affiliation: Department of Physics, University of Allahabad
Conference ID: ASI2017_1159
Title : Multi-wavelength Investigations of Solar Eruptive Phenomena
Authors and Co-Authors : Dr. Bhuwan Joshi, Udaipur Solar Observatory, Physical Research Laboratory, Udaipur, 313001
Abstract Type : Thesis
Abstract Category : Thesis
Abstract : Solar eruptive phenomena correspond to various kind of transient activities occurring in the solar atmosphere in the form of flares, prominence eruptions and coronal mass ejections. They mostly originate from solar active regions which consist of complex magnetic structures extending from the deeper sub-photospheric layers, crossing through the photosphere to the coronal heights. An eruptive flare typically spreads across all the atmospheric layers of the Sun and involves substantial mass motions and particle acceleration. Multi-wavelength observations are thus crucial to probe the underlying physical processes occurring at different layers and regions at and above the photosphere. In my thesis, we have studied some key aspects of solar eruptive phenomena such as solar flare, prominence eruption, coronal implosion, failed eruption, and sigmoid-to-arcade evolution. These investigations have employed contemporary multi-wavelength solar observations with superior resolution. The imaging and spectroscopic capabilities of Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) have been extensively utilized to investigate the thermal and non-thermal energy release processes associated with different stages of the eruptive phenomena. Complementary to RHESSI X-ray measurements, we have combined solar observations at Extreme Ultraviolet (EUV), Ultraviolet (UV), Microwave (MW), optical, and radio wavelengths to investigate the complex physical processes occurring at different atmospheric layers of the Sun during the eruptive events. Some of the major highlights are given below: 1. We find striking evidence of ongoing magnetic reconnection in the form of an extended HXR coronal source at 50–100 keV energy band which developed during the detachment of an erupting prominence from the solar source region. This phase of intense coronal emission was associated with high plasma temperature (T~30 MK) and significant non-thermal charac- teristics. 2. We have carried out a detailed study of flux evolution through the active region in relation to triggering of an impulsive M4.0 flare. We have adopted a new approach to investigate the characteristics of magnetic transients by analyzing HMI spectral data. We find that the sudden changes in the small-scale magnetic field have likely triggered the flare by destabilizing the highly sheared pre-flare magnetic configuration. 3. We have investigated the role of pre-flare activities toward the destabilization of magnetic configuration of pre-flare corona which lead to a large-scale eruptions and associated flares. 4. We have detected a large-scale contraction of coronal loops for ~30 minutes during the pre- flare phase of an M6.2 flare in active region NOAA 10646. Such a large-scale contraction has been observed for the first time during which the loop system was subjected to an altitude decrease of ~40% of its initial height. 5. Finally, we have investigated the sigmoid-to-arcade evolution and discussed their observational disparities with the standard flare model.