Tracking Prominence Eruptions to 1 AU with STEREO Heliospheric Imaging

Abstract:

It is rare for prominence eruptions to be observable far from the Sun in the inner heliosphere, either in imaging or with in situ plasma instruments. Nevertheless, we here discuss two examples of particularly bright eruptions that are continuously trackable all the way to 1 AU by imagers on the Solar TErrestrial RElations Observatory (STEREO) spacecraft. The two events are from 2011 June 7 and 2012 August 31. Only these two examples of clear prominence eruptions observable this far from the Sun could be found in the STEREO 2007-2014 image database, consistent with the rarity of unambiguous cold prominence material being observed in situ at 1 AU. Full 3-D reconstructions are made of the coronal mass ejections (CMEs) that accompany the prominence eruptions. For the 2011 June event, a time-dependent 3-D reconstruction of the prominence structure is made using point-by-point triangulation, which unfortunately is not possible for the August event due to a poor viewing geometry. However, for the 2012 August event, shock normals computed from plasma measurements at STEREO-B and Wind using the shock jump conditions agree well with expectations from the image-based CME reconstruction. Unlike its accompanying CME, the 2011 June prominence exhibits little deceleration from the Sun to 1 AU, as a consequence moving upwards within the CME. Detailed analysis of the prominence’s expansion reveals that deviation from self-similar expansion is never large, but close to the Sun the prominence expands somewhat more rapidly than self-similarity, with this effect decreasing with time.