Heliophysics Division, NASA Goddard Space Flight Center
The Onset of Magnetic Reconnection
Many phenomena on the Sun, within the heliosphere, and throughout the universe involve the explosive release of magnetic energy. Magnetic reconnection is the process by which this occurs. A fundamental property of reconnection that is not well understood is its "switch on" nature. It must remain switched off to allow magnetic stresses to slowly build to sizable levels and then suddenly switch on to release the stored energy. If reconnection were operating efficiently all the time, events like solar flares and coronal mass ejections would be weak, and nanoflares would not be able to maintain the hot temperatures of the corona. The onset of magnetic reconnection generally begins with the unstable tearing of electric current sheets. I will discuss recent magnetohydrodynamic (MHD) simulations showing how the nonlinear development of the tearing, which controls how much energy is ultimately released, depends crucially on the length, width, and shear angle of the current sheet. We have identified three distinct and predictable evolutionary paths that are set by the relative growth rates of the parallel and oblique modes of the initial linear tearing. I will discuss these new findings and their relevance to solar phenomena.