  The Solar TErrestrial RElations Observatory (STEREO) provides high cadence
and high resolution images of the structure and morphology of coronal mass
ejections (CMEs) in the inner heliosphere. CME directions and propagation
speeds have often been estimated through the use of time-elongation maps
obtained from the STEREO Heliospheric Imager (HI) data. Many of these CMEs have
been identified by citizen scientists working within the SolarStormWatch
project ( www.solarstormwatch.com ) as they work towards providing robust
real-time identification of Earth-directed CMEs. The wide field of view of HI
allows scientists to directly observe the two-dimensional (2D) structures,
while the relative simplicity of time-elongation analysis means that it can be
easily applied to many such events, thereby enabling a much deeper
understanding of how CMEs evolve between the Sun and the Earth. For events with
certain orientations, both the rear and front edges of the CME can be monitored
at varying heliocentric distances (R) between the Sun and 1 AU. Here we take
four example events with measurable position angle widths and identified by the
citizen scientists. These events were chosen for the clarity of their structure
within 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) and
the 2D aspect ratio (X) of these CMEs, which are measured out to ~0.7 AU. We
estimated the radial width from a linear best fit for the average of the four
CMEs. We obtained the relationships W=0.14R+0.04 for the width and X=2.5R+0.86
for the aspect ratio (W and R in units of AU).
