CME Evolution Characteristics in the Inner Heliosphere Observed Using SMEI and STEREO/SECCHI/HI Data

Geometric and propagation characteristics of interplanetary coronal mass ejections (ICMEs) are investigated using data obtained by the Large Angle Spectroscopic Coronagraph (LASCO), the Solar Mass Ejection Imager (SMEI) and the SECCHI imaging experiments on each STEREO spacecraft. The early evolution of CMEs can be tracked by the LASCO C2 &\ C3 and SECCHI COR1 &\ COR2 coronagraphs and the HI instruments can view them further into the heliosphere. SMEI is an all-sky imager that has tracked ICMEs from elongations >20° to beyond 100°. Both HI and SMEI hence have the ability to observe the same transient at the same time. We present results for ICMEs observed on 24--29 January and February through May 2007. This includes measurements of the structural and kinematic evolution of ICMEs and comparison with an appropriate drive/drag model. Crucial to the analysis procedure is an understanding of the effects of projection across large distances, which are not generally required with coronagraph data. Also discussed is the physics behind the evolution of ICMEs at large distances from the Sun, including the required inclusion of an internal driving force for some ICMEs, which sustains the transient's high speed well into the interplanetary medium.