Kinematics of Coronal Mass Ejections in the Inner Corona and its Coupling with the Heliosphere

Abstract

Ever since the dawn of astronomy, we and the Sun have not been celestial strangers anymore, and it was soon realised that there is a close Sun-Earth connection that was awaiting our acknowledgement. With that came several dedicated space and ground based solar missions, and it was understood that Coronal Mass Ejections (CMEs) lies at the heart of this Sun-Earth connection. After several decades of observing and studying CMEs, our understanding of their behaviour have touched great heights. But, inspite of the strident progress in this area, there are some challenges that have left certain grey patches in our understanding of CMEs. Although we do have a good understanding of the propagation of the CME in the outer corona and the heliosphere, we are yet to have a clear understanding of the early evolutionary phase of the CMEs in the inner corona region (< 3R⊙). This has been mainly due to limited observational data in the inner corona, and projection effects occurring due to measurements made on the plane of the sky. This thesis particularly aims at improving our understanding on the above two aspects, and dedicates the results obtained to several existing and upcoming solar missions that will be observing the inner corona. As an attempt to remove projection effects and to understand the kinematics of CMEs in the inner corona, the Graduated Cylindrical Shell (GCS) model is applied on the stereoscopic observations of 59 CMEs from COR-1 and COR-2 on-board the twin spacecraft Solar Terrestrial Relations Observatory (STEREO-A/B). This enabled a two vantage point tracking of CMEs through a combined field of view of 1.5 - 14 R⊙. We combined the 3D width evolution and acceleration profiles to report for the first time an observational evidence in support of the conjecture that CME acceleration and width expansion are just different manifestations of the same Lorentz force, and based on this we report that statistically, the Lorentz force impact on the kinematics remains dominant in a height range of 2.5 - 3 R⊙. We also show that combining latitude and position angle distributions to understand CME deflections, might be misleading. With a statistical study on the distribution of projected widths of CMEs, we report for the first time that slow (< 300 kms−1) and fast (> 500 kms−1) CMEs arising from different source regions (i.e. active regions (ARs) and prominence eruptions (PEs)) follow different power laws in their width distributions, thus indicat ing different physical mechanisms of width expansion. We also study the coupling of the 3D kinematics in the inner corona, to the kinematics in the outer corona, and we find that the kinematics in the inner corona largely controls the later kinematics, and that this coupling of kinematics is different for CMEs arising from ARs and PEs. We report on several statistical correlations between different kinematic parameters in the inner and outer corona, and we present empirical relations that can be used in extrapolating outer coronal parameters from inner coronal parameters. But, owing to the limited field of view of COR-1, the full main acceleration phase of the CME could not be captured, because a part of that crucial phase was already over by the time the CME came in the COR-1 field of view. Further, due to 2 vantage point tracking, there are degeneracy in certain parameters for some CME orientations. Motivated by the above results and the shortcomings that came along, we extended the application of the GCS model to the inner coronal observations from the ground–based coronagraph K–Cor of the Mauna Loa Solar Observatory (MLSO) along with the pair of observations from STEREO as earlier. This Extended - GCS (EGCS) model enabled for the first time 3D tracking of CMEs, uniquely in white light observations from heights as low as 1.1 R⊙. Apart from being able to capture the early acceleration phase of the CMEs in white light observations, we also studied the evolution of the true volume of the CME with height. For the first time, we report a a power law dependence of the CME volume with distance from the Sun. We further find the volume of ellipsoidal leading front and the conical legs follow different power laws, thus indicating differential volume expansion through a CME. The study also reveals two distinct power laws for the total volume evolution of CMEs in the inner and outer corona, thus suggesting different expansion mechanisms at these different heights. Also, this differential volume expansion of CMEs further motivated me in studying the velocity dispersion inside CMEs in the inner corona, as that will have profound significance on the validity of the assumption of self-similar expansion of CME evolution. A multi-wavelength study is also presented here on a CME that occurred on January 26 2014. In this work, the significance of combining radio observations with white-light and extreme ultraviolet observations is presented in better understanding the shock driving phenomenon of CMEs that are responsible for producing type-II radio bursts. It was with the help of the radio spectral and imaging observations, that it became possible to pin point that it was the flank of the CME than the nose, that hosted the type-II burst location, and that too, the Southern flank. Encapsulating in a nutshell, this thesis will largely aid in filling in some of the crucial gaps and connect the missing links (as mentioned earlier) towards a holistic understanding of CME kinematics in inner corona, and the way the kinematics gets coupled at the higher heights. The different chapters besides highlighting the sole potential of white-light observations in arriving at the above scientific goals, will also provide rich inputs in observational plannings of the existing and upcoming solar missions that will observe the inner corona. It will also provide crucial constraints to the models that tries to emulate the ejection and propagation of CMEs at the lower and higher heights.