CME reconstruction: Pre-STEREO and STEREO era

Since the first observations of coronal mass ejections (CMEs) in 1970s, their three-dimensional (3D) morphology has been a key ingredient for understanding their origin and evolution. The determination of their 3D structure using a single viewpoint, however posed a challenge because only their 2D projection on the sky plane is observed. The operation of the STEREO mission with its unique capability of imaging the inner heliosphere from two viewpoints has greatly improved this situation. It is therefore timely to review the pre-STEREO efforts in 3D CME reconstruction and compare them with the first STEREO results in this area. Our paper focuses on the techniques relevant to the CME morphology: forward modeling, polarimetric, spectroscopic, direct inversion. We also discuss the limitations and considerations involved in each technique.

Research Highlights
► Review of CME reconstruction techniques: forward modeling, polarization, spectroscopic and tomographic.
► STEREO data confirmed that most of the CMEs could be modeled using hollow croissant type morphology.
► Reconstruction of the fine details of the CME morphology are not yet achieved.
► Future study should strive to combine different techniques and merge data from different sensors.