Bridging EUV and White-Light Observations to Inspect the Initiation Phase of a "Two-Stage" Solar Eruptive Event

The initiation phase of coronal mass ejections (CMEs) is a very important aspect of solar physics, as these phenomena ultimately drivespace weather in the heliosphere. This phase is known to occur betweenthe photosphere and low corona, where many models introduce aninstability and/or magnetic reconnection that triggers a CME, often withassociated flaring activity. To this end, it is important to obtain avariety of observations of the low corona to build as clear a picture aspossible of the dynamics that occur therein. Here, we combine the EUVimagery of the Sun Watcher using Active Pixel System Detector and ImageProcessing (SWAP) instrument onboard the Project for Onboard Autonomy(PROBA2) with the white-light imagery of the ground-based Mark-IVK-coronameter (Mk4) at Mauna Loa Solar Observatory (MLSO) to bridge theobservational gap that exists between the disk imagery of theAtmospheric Imaging Assembly (AIA) onboard the Solar DynamicsObservatory (SDO) and the coronal imagery of the Large AngleSpectrometric Coronagraph (LASCO) onboard the Solar and HeliosphericObservatory (SOHO). Methods of multiscale image analysis were applied tothe observations to better reveal the coronal signal while suppressingnoise and other features. This allowed an investigation into theinitiation phase of a CME that was driven by a rising flux-ropestructure from a "two-stage" flaring event underlying an extended helmetstreamer. It was found that the initial outward motion of the eruptingloop system in the EUV observations coincided with the first X-ray flarepeak and led to a plasma pile-up of the white-light CME core material.The characterized CME core then underwent a strong jerk in its motion,as the early acceleration increased abruptly, simultaneously with thesecond X-ray flare peak. The overall system expanded into the helmetstreamer to become the larger CME structure observed in the LASCOcoronagraph images, which later became concave-outward in shape.Theoretical models for the event are discussed in light of these uniqueobservations, and it is concluded that the formation of either akink-unstable or torus-unstable flux rope may be the likeliest scenario.