Dr. Spiro K.Antiochos (U Michigan & NASA/GSFC)
30 January 2025
11:30, Aula Piazzi
Abstract:
The Sun’s atmosphere, the corona, is characterized by ubiquitous bursts of energy release ranging from giant coronal mass ejections (CMEs) and flares that are the largest explosions in our solar system, to the orders of magnitude smaller coronal jets and bright points that are responsible for much of the mass and energy of the solar wind. All these forms of solar activity share the common underlying origin that, as a result of stressing by the subsurface convective flows, magnetic free energy first builds up in the corona and then is released impulsively to the plasma in the form of heating, mass motions, and/or particle acceleration. We present high-resolution observations from NASA/ESA/JAXA space missions showing that the energy buildup and release appears to be similar for eruptive activity ranging across orders of magnitude in scale and energy. From the observations it is possible to infer the basic nature of solar eruptions, but the physical mechanisms responsible for the onset and large energy release are still unclear. We discuss the current theories for eruption onset and present the latest MHD numerical simulations that include self-consistently both the energy buildup and explosive release. The models show that current sheet formation leading to magnetic reconnection and energy release occurs almost continuously in the corona, but explosive energy release occurs only when there is strong feedback between the reconnection and the global ideal evolution. Modeling this multiscale feedback accurately remains as the greatest challenge to understanding and eventually predicting solar activity.