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The Solar TErrestrial RElations Observatory (STEREO) provides high cadenceand high resolution images of the structure and morphology of coronal massejections (CMEs) in the inner heliosphere. CME directions and propagationspeeds have often been estimated through the use of time-elongation mapsobtained from the STEREO Heliospheric Imager (HI) data. Many of these CMEs havebeen identified by citizen scientists working within the SolarStormWatchproject ( www.solarstormwatch.com ) as they work towards providing robustreal-time identification of Earth-directed CMEs. The wide field of view of HIallows scientists to directly observe the two-dimensional (2D) structures,while the relative simplicity of time-elongation analysis means that it can beeasily applied to many such events, thereby enabling a much deeperunderstanding of how CMEs evolve between the Sun and the Earth. For events withcertain orientations, both the rear and front edges of the CME can be monitoredat varying heliocentric distances (R) between the Sun and 1 AU. Here we takefour example events with measurable position angle widths and identified by thecitizen scientists. These events were chosen for the clarity of their structurewithin the HI cameras and their long track lengths in the time-elongation maps.We show a linear dependency with R for the growth of the radial width (W) andthe 2D aspect ratio (X) of these CMEs, which are measured out to ~0.7 AU. Weestimated the radial width from a linear best fit for the average of the fourCMEs. We obtained the relationships W=0.14R+0.04 for the width and X=2.5R+0.86for the aspect ratio (W and R in units of AU).

Observational Tracking of the 2D Structure of Coronal Mass Ejections Between the Sun and 1 AU