A synoptic view of solar transient evolution in the inner heliosphere using the Heliospheric Imagers on STEREO

By exploiting data from the STEREO/heliospheric imagers (HI) we extend a well‐established technique developed for coronal analysis by producing time‐elongation plots that reveal the nature of solar transient activity over a far more extensive region of the heliosphere than previously possible from coronagraph images. Despite the simplicity of these plots, their power in demonstrating how the plethora of ascending coronal features observed near the Sun evolve as they move antisunward is obvious. The time‐elongation profile of a transient tracked by HI can, moreover, be used to establish its angle out of the plane‐of‐the‐sky; an illustration of such analysis reveals coronal mass ejection material that can be clearly observed propagating out to distances beyond 1AU. This work confirms the value of the time‐elongation format in identifying/characterising transient activity in the inner heliosphere, whilst also validating the ability of HI to continuously monitor solar ejecta out to and beyond 1AU.