Driving mechanisms of magnetic energy release phenomena, flares and CME at various stages of solar/stellar cycles

Shibata Kazunari, shibata@kwasan.kyoto-u.ac.jp, Kwasan and Hida Observatory, Kyoto University


Abstract
Recent development of observations of solar flares and coronal mass ejections (CMEs) have revealed that the central engine of solar flares/CMEs is magnetic reconnection and associated magnetohydrodynamic processes. At present, the following fundamentall questions are remained unsolved: 1) What determines the reconnection rate (or energy release rate) in flares/CMEs ? 2) What is the triggering mechanism of reconnection (or flares/CMEs) ? 3) What is the particle acceleration mechanism in flares/CMEs ? First we will review the present status of the research to study these questions. At present, it seems that multiple plasmoid ejections and associated multiple (or multi-step) reconnection might play a key role to lead to fast reconnection and associated particle acceleration. Emerging flux also appears to play a key role in triggering major energy release through multi-step reconnection. Then we will discuss stellar flares. Recent progress of stellar flare observations revealed various common properties between solar and stellar flares, and it seems that stellar flares are also driven by the same magnetohydrodynamic mechanism as that of solar flares, containing reconnection as a central engine. We present unified model of solar and stellar flares based on reconnection model and related new observations. Finally we will discuss the possibility of superflares on the present Sun on the basis of recent Kepler observations of superflares on solar type stars.