On 3D reconstruction of coronal mass ejections: II. Longitudinal and latitudinal width analysis of 31 August 2007 event

In an earlier work, Mierla et al. (2009) applied four different reconstruction techniques to three coronal mass ejections (CMEs) at a given time. This study is a follow up of the above work in which we apply a local correlation tracking and tie-point reconstruction technique (LCT–TP) to the CME observed on 31 August 2007 by the COR1 and COR2 coronagraphs onboard the STEREO spacecraft at different times. The results show considerable scatter in the direction parallel to the line of sight, which is a direct indication of the CME depth. We derive the longitudinal and latitudinal sizes of the CME as a function of time. We find that a reasonable lower estimate of the longitudinal size is 18°–44° with an absolute largest extent of 78°–110°. We also find that a reasonable lower estimate for the latitudinal size of the CME is 18°–32° with an absolute largest extent of 44°–56°. In general, the latitudinal size is smaller than the longitudinal size, indicating an elliptical cone like structure or a flux rope like structure with very little tilt relative to the ecliptic. Self-similar expansion is observed above a height of 6.9R⊙6.9R⊙. As our analysis is based on a statistical approach, large scatter is expected. In order for the method to be validated, more cases have to be studied.

Research Highlights
► Three-dimensional reconstruction of a structured coronal mass ejection is performed.
► Longitudinal and latitudinal extents of the ejection are derived.
► The results indicate an elliptical or a flux rope like structure.
► Self-similar expansion is observed above a height of 6.9 solar radii.