Reconstructing the Morphology of an Evolving Coronal Mass Ejection
NAVAL RESEARCH LAB WASHINGTON DC SPACE SCIENCE DIV
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Using imaging data from the STEREO mission, we empirically reconstruct the time-dependent three-dimensional morphology of a coronal mass ejection CME from 2008 June 1, which exhibits significant variation in shape as it travels from the Sun to 1 AU, requiring us to abandon the assumption of self-similar expansion. We model the CME as a flux rope that is rather fat relative to its longitudinal extent close to the Sun, but which becomes thinner and flatter on top as the flux rope moves outwards. We find best agreement with the STEREO images when the flux ropes west leg is assumed to be rotated 35 deg below the ecliptic plane. This orientation is consistent with previously published inferences about this CMEs orientation from an analysis of in situ observations of the event from June 6-7, when the CME hits STEREO-B. The agreement between these two very different kinds of analysis is encouraging. Close to 1 AU the CME not only hits STEREO-B but also strikes a comet Comet C2007 W1 Boattini, which provides an additional constraint for our reconstruction efforts. Finally, we find that this CME is very instructive for assessing different methods of extracting kinematic information from measurements of elongation angles from the Sun, which is a complicated issue for measurements far from the Sun. The Fixed-theta assumption that we have used successfully in the past does not work well here, and we discuss the implications for extracting reliable kinematic information from heliospheric imaging.