The Structural Connection between Coronal Mass Ejection Flux Ropes near the Sun and at 1 au

Abstract

Abstract We have performed the first comprehensive statistical analysis comparing flux rope (FR) structures of coronal mass ejections (CMEs) near the Sun and at 1 au, using Solar and Heliospheric Observatory and Solar Terrestrial Relations Observatory measurements for the two full solar cycles 23 and 24. This study aims to investigate the physical connection of 102 magnetic FRs among solar source regions, CMEs in the extended corona, and magnetic clouds (MCs) near Earth. Our main results are as follows: (1) We confirmed that the hemispheric-helicity rule holds true for ∼87% of our 102 events. For the 13 events that do not follow this rule, the FR axis directions and helicity signs can be inferred from soft X-ray and extreme ultraviolet images and magnetogram data in the source regions (e.g., coronal arcade skews, Fe xii stalks, sigmoids, and magnetic tongues). (2) Around 25% of the 102 events have rotations >40° between the MC and CME-FR axial orientations. (3) For ∼56% of these rotational events, the FR rotations occurred within the COR2 field of view, which can be predicted from the CME tilts obtained from FR fitting models. In addition, we found that for 89% of the 19 stealth CMEs under study, we were able to use coronal neutral line locations and tilts to predict the FR helicity and its axial direction in the MCs. The above results should help improve the prediction of FR structures in situ. We discuss their implications on space weather forecasts.