Authors: Eleni Nikou (NRC Research Associate, U.S. Naval Research Laboratory), Robin Colaninno (U.S. Naval Research Laboratory), Phillip Hess (U.S. Naval Research Laboratory), Angelos Vourlidas (Johns Hopkins University, Applied Physics Laboratory), Jie Zhang (George Mason University)

Coronal mass ejections (CMEs) originate from the Sun and are the main driver of space weather. Their radial and lateral evolution are essential in understanding the physics behind them as well as for space weather predictions. It is understood that their radial evolution consists of three phases, the initiation, acceleration and propagation phases. CMEs overexpand laterally close to the Sun transitioning to a self-similar expansion at larger heights. In this study we investigate the morphological evolution of CMEs from the inner to the outer corona using a 3D minimization based fitting technique that applies the graduated cylindrical shell (GCS) model on multi-viewpoint observations from the inner corona by EUVI and COR1, and outer corona by COR2 onboard the twin STEREO spacecraft, and returns the GCS geometric parameters along with their uncertainties. We investigate whether the CMEs expand in a self-similar way by calculating the expansion rate of the ejecta. Finally, we analyze the uncertainties of the GCS geometric parameters from a single viewpoint and how they change when a second viewpoint is added.