Coronal mass ejections (CMEs) are massive eruptions of magnetised plasma that is believed to be originated from the solar corona. CMEs are known to play a significant role in driving disastrous space weather. This thesis focuses on understanding the dynamics of CMEs source regions with the observations made by STEREO, the Solar Terrestrial Relations Observatory. The successful launch of STEREO provides us with the first-ever stereoscopic measurements to study the 3D structures of CMEs. With the data from Extreme Ultra-Violet Imager (EUVI) and coronagraphs COR1 and COR2 onboard both STEREO Ahead (A) and STEREO Behind (B) and the data from other instruments, we studied of the initiation of a CME and its associated phenomena. The CME occurs on 2007 December 7, during which the separation angle of STEREO A with B is about 42.4◦ . This offers us a good opportunity to study the initiation of the CME stereoscopically. Using the data from both STEREO A and B, we made a detailed comparison for the morphologies and kinematics of its associated “EIT wave”. The results indicate that the nascent CME seems to affect the morphology of the EIT wave, vise verse, i.e., the morphology of EIT wave reflects the morphology of the CME. Taking the advantage of the two viewpoints of the STEREO spacecrafts from January 1 to August 31, 2009, we identified 34 CMEs that originated from almost one quarter of the Sun which faces the Earth. It is found that about 33 % of them had no distinct low coronal signature (such as coronal dimming, coronal wave, filament eruption, post-eruptive arcade). It might be a new challenge for our present models of CME origination. What is the trigger for the CMEs without no distinct low coronal signature? Is there any difference between the two kinds of CMEs? What is the implication for CME prediction? These questions are discussed in this thesis.
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