Dynamics of coronal transients as seen from space observations

Abstract

The thesis is focused on the study of the coronal transients at different spatial and tem- poral scales seen in different layers of the solar atmosphere using space-based imaging

and spectroscopic instruments. The first part of the thesis is focused on the study of the dynamics of the small-scale coronal transients found in the solar atmosphere. We explored the interaction between different small-scale transients observed in different layers of the solar atmosphere. We studied the role of small-scale transients (transition region jets) in sustaining the propagating disturbances (PDs) in the coronal plumes. We explored the connection between transition region (TR) jets and the propagating disturbances (PDs) seen in an on-disk plume combining the observations of Interface Region Imaging Spectrograph (IRIS) and Solar Dynamics Observatory (SDO). We demonstrated that the PDs in plumes are the signatures of the slow magnetoacoustic waves which are connected with the reconnection outflows at the supergranulation boundaries, i.e, TR jets. We presented one-to-one correspondence between TR jets and PDs at the footpoint of the plume. We studied long-period (60 minutes) transverse oscillations in a coronal loop triggered by a coronal jet which carries much less energy than CMEs or blast waves. We found that the jet consisted of hot and cool components. Hot component of jet interacted with the coronal loop and triggered transverse oscillations. We estimated the energy density inside the loop and found that it was large enough to sustain the transverse oscillations. Thus we inferred that the coronal jet triggered the long-period transverse oscillations in the coronal loop. We studied the quasi-periodic intensity disturbances of 20–25 minutes periodicity in

the open magnetic structures such as fan loops. We showed that these intensity dis- turbances were the signatures of standing oscillations that were excited by transients

such as EUV waves (blast waves) originating at a distant active region. This is the first observation of standing oscillations in the coronal fan loops. Though, standing oscillations in the hot coronal loops (T∼10 MK) were reported earlier.

The second part of the thesis is focused on the study of the large-scale coronal tran- sients, ı.e., coronal mass ejections (CMEs). CMEs are the large-scale eruptions of

magnetic field and plasma from the atmosphere of the Sun to the heliosphere. Several automated detection algorithms exist to detect CMEs automatically in the coronagraph

images. However, these methods could not be successfully implemented for detect- ing CMEs/ICMEs in heliosphere using inner Heliospheric Imager (HI-1) images due

to heavy contamination of stars and planets. We developed an automated detection

algorithm to detect CMEs in heliosphere using the data from HI-1 onboard Solar Ter- restrial Relations Observatory (STEREO). We used the principle of Hough transform

as implemented in Computer Aided CME tracking (CACTus) to detect CMEs in HI-1 images. We found that the output of automated catalog matches well with the manual catalog. The catalog is now running on real-time and is available for public use. Finally, we studied the kinematics of fast and slow CMEs in solar cycle 23 and 24 using Coordinated Data Analysis Workshops (CDAW) and CACTus catalogs that list the properties of CMEs, which are manually and automatically identified, respectively, using Large Angle and Spectrometric Coronagraph (LASCO) C2 and C3 images. The width distribution of the CMEs is believed to follow a power law with power index of ∼-1.7. We reported that fast and slow CMEs have different power laws which could be due to their different energy sources. We also studied the rate of occurrences in the slow and fast CMEs in solar cycles 23 and 24. We found that cycle 24 is producing

more slower CMEs as compared to cycle 23, which could be due to the weak helio- spheric field.