Initiation And Early Kinematic Evolution Of Solar Eruptions

Solar eruptions include coronal mass ejections (CMEs) and solar flares that are the most energetic eruptive phenomena in the solar system and are able to produce severe impacts on human high-tech activities in outer space. Nevertheless, the key questions of how and when CMEs/flares are initiated are still puzzled. In this talk, I will present a detailed analysis of the early kinematics of 12 solar eruptions, which yields three main conclusions: (1) The early evolution of all events consists of a slow-rise phase followed by a main-acceleration phase, the height-time profiles of which differ markedly and can be best fit, respectively, by a linear and an exponential function. This indicates that different physical processes dominate in these phases, which is at variance with models that involve a single process. (2) The kinematic evolution of the eruptions tends to be synchronized with the flare light curve in both phases. But, a delayed onset of the impulsive flare phase is found in the majority of the filament eruptions. This delay, and its trend to be larger for slower eruptions, favor ideal MHD instability models. (3) The average decay index at the onset heights of the main acceleration is close to the threshold of the torus instability for both groups of events, suggesting that this instability initiates and possibly drives the main acceleration.