Initiation of solar flares: reconnection, heating, particle acceleration -Final Report

Summary

Flares and coronal mass ejections (CMEs) from the Sun are the most energetic processes in our solar system. The high radiation, fast particles and magnetic field carried by these eruptions are the major sources of severe disturbances of our space weather at Earth. Magnetic reconnection is a fundamental process in magnetized plasmas, which drives these energetic events. The overall goal of the research project was to perform systematic studies of the pre- and early phase of solar flares, in order to better understand how magnetic reconnection is initiated in flares, how the released energy is converted into different forms, and how these processes are related to CME eruptions. Our main results are the following:

• We provide the first comprehensive and comparative description of the properties of flares with/without associated CME, with all the main factors involved: the properties of the source active region, the flare location within the active region, and the evolution and properties of the flare ribbons.
• We derived an estimate of the largest flare that can be produced by the present day’s Sun, which is of the order of GOES X100, i.e. about a factor of 3 bigger than then largest flares observed in the satellite era but on the lower limit of “superflares” recently detected on solar-like stars.
• For the first time, the micro-processes that build up CME eruptions have been revealed in observations, thus bridging the gap between the CME microscale and macroscale dynamics. We demonstrate how a CME evolves from the detachment and merging of multiple plasmoids, i.e. mini flux ropes that are barely resolved.
• Our studies challenge the traditional interpretation of the CME three-part morphology where the core corresponds to the erupting prominence. We demonstrate that in some strong events the core is a manifestation of the magnetic flux and frozen-in plasma added to the rising flux rope by flare-related magnetic reconnection and serving for its acceleration.
• We derived a method to better separate the thermal and non-thermal emission in solar flares, which is important for the characterization of particle acceleration in solar flares and the atmospheric response to the impulsive energy input.