Bridging EUV and white-light observations to inspect the initiation phase of a "two-stage" solar eruptive event

Abstract

The initiation phase of CMEs is a very important aspect of solar physics, as these phenomena ultimately drive space weather in the heliosphere. This phase is known to occur between the photosphere and low corona, where many models introduce an instability and/or magnetic reconnection that triggers a CME, often with associated flaring activity. To this end, it is important to obtain a variety of observations of the low corona in order to build as clear a picture as possible of the dynamics that occur therein. Here, we combine the EUV imagery of the SWAP instrument on board PROBA2 with the white-light imagery of the ground-based Mk4 coronameter at MLSO in order to bridge the observational gap that exists between the disk imagery of AIA on board SDO and the coronal imagery of LASCO on board SOHO. Methods of multiscale image analysis were applied to the observations to better reveal the coronal signal while suppressing noise and other features. This allowed an investigation into the initiation phase of a CME that was driven by a rising flux rope structure from a "two-stage" flaring active region underlying an extended helmet streamer. It was found that the initial outward motion of the erupting loop system in the EUV observations coincided with the first X-ray flare peak, 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, simultaneous with the second X-ray flare peak. The overall system expanded into the helmet streamer to become the larger CME structure observed in the LASCO coronagraph images, which later became concave-outward in shape. Theoretical models for the event are discussed in light of these unique observations, and it is concluded that the formation of either a kink-unstable or torus-unstable flux rope may be the likeliest scenario.

21 pages, 9 figures, 3 movies

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• Torus instability
• Ideal kink instability of a magnetic loop equilibrium
• Observations of an extreme storm in interplanetary space caused by successive coronal mass ejections
• Multi-scale Gaussian normalization for solar image processing
• Propagation of an Earth-directed coronal mass ejection in three dimensions
• Observations and modeling of the early acceleration phase of erupting filaments involved in coronal mass ejections
• The Depiction of Coronal Structure in White Light Images
• Quasiperiodic acceleration of electrons by a plasmoid-driven shock in the solar atmosphere
• Automatic Detection and Tracking of CMEs II: Multiscale Filtering of Coronagraph Data
• The kinematics of coronal mass ejections using multiscale methods
• Multiscale Edge Detection in the Corona
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• Observations of an Eruptive Solar Flare in the Extended EUV Solar Corona
• Observations of the Formation, Development, and Structure of a Current Sheet in an Eruptive Solar Flare
• Observations of the Coronal Mass Ejection with a Complex Acceleration Profile
• Expanding and Contracting Coronal Loops as Evidence of Vortex Flows Induced by Solar Eruptions
• Solar Total Eclipse of 21 August 2017: Study of the Inner Corona Dynamical Events Leading to a CME