Connections between CME leading fronts and erupting filaments/cavities
Joe Hutton
Aberystwyth University
Huw Morgan (Aberystwyth University)
The three-part structure of CMEs (inner core, cavity and bright leading edge) is believed to arise from the flux-rope structure of the erupting filament and associated cavity. This is not easy to show directly due to the lack of clean observations of the inner corona between 1.3 solar radii (approximate field of view limit of EUV imagers) and 2.2 solar radii (inner field of view of LASCO C2). A survey of filament eruptions observed in EUV by SDO's AIA and STEREO's EUVI instruments from May 2013 to June 2014 are processed with the new Multi-scale Gaussian Normalisation (MGN) technique, with case events presented. Processing of EUV images reveals loop-like structures existing above the filament long prior to the eruption. The result of the survey shows that at least 30% of flux-rope CMEs have pre-existing loops over the associated filament, forming the front edge of the 3-part structure. To further confirm the link between cavity loops and CME fronts in a few case studies, the kinematics of a flux-rope density model is constrained by the data and the resulting images compared to observation. There are several observational reasons why pre-existing systems of loops cannot always be detected in EUV images, leading to our tentative conclusion that CME leading fronts are the outer boundaries of a pre-existing large flux tube that surround the filaments and which expand outwards with the eruption.