During magnetic reconnection, the energy stored in magnetic fields is quickly tapped and converted into heat and kinetic energy, in a process analogous to a magnetic explosion. Reconnection is thought to power many astrophysical events including solar flares and Earth's auroras, as well as play an important role in laboratory fusion experiments. Although the basic workings of magnetic reconnection are well-understood, a long-standing puzzle has existed as to the precise process that provides the spark triggering the explosion. Advances in computer power have recently made it possible to model magnetic reconnection in three dimensions and allow this work to answer the question.
By tapping the energy of magnetic fields, reconnection in the solar corona and solar wind drives space weather, the changing of environmental conditions in near-Earth space. Space weather, in turn, has profound influences on topics as diverse as passenger radiation exposure on polar flights, communications satellite lifetimes, and the stability of electrical power grids. Exploring the dynamics of reconnection and, in particular, understanding the processes that allow reconnection to occur thus has broad importance for society.
Magnetic fields are a significant, and sometimes the primary, reservoir of energy in many astrophysical phenomena. During the process known as magnetic reconnection, this energy is quickly tapped and converted into the kinetic energy of particles. Reconnection in the solar corona and solar wind drives space weather, the changing of environmental conditions in near-Earth space. Space weather, in turn, has profound influences on topics as diverse as passenger radiation exposure on polar flights, communications satellite lifetimes, and the stability of electrical power grids. Exploring the dynamics of reconnection and, in particular, understanding the processes that allow reconnection to occur thus has broad importance for society as a whole. Although the basic workings of magnetic reconnection are well-understood, the precise mechanisms that serve as the trigger and accelerate particles are still open questions. Since laboratory experiments and in situ satellite observations of reconnection are difficult (although it is the focus of NASA's upcoming Magnetospheric Multiscale Mission), computer simulations offer a complementary approach. The most physically accurate formulations require massive amounts of computational power and only with recent supercomputers has it become possible to compute physically accurate models in three dimensions. The primary goal of this project was to understand, via numerical simulations, the mechanisms responsible for sparking magnetic reconnection. Answering this question would further our knowledge of this fundamental process. Future work, e.g., global simulations of space weather, can incorporate the findings which would allow for better predictions and protection against adverse events. Reconnection occurs in what are known as plasmas, collections of charged particles, usually protons and electrons, in which a magnetic field is embedded. Work for this project has found that during reconnection (and particularly during a quite common type known as guide-field reconnection), thin regions of current can form, become unstable, and evolve into turbulence. A phenomenon known as anomalous viscosity (an electromagnetic analogue of the usual fluid viscosity) becomes important in such turbulent regions and the simulations and analysis we have performed show that it is the dominant mechanism triggering reconnection over a broad range of parameters. The accompanying image shows results from one of the simulations. Oppositely-directed magnetic field lines (red, orange, and white) reconnect at the central current layer. Numerous flux ropes (seen in the isosurfaces as red on the ends with a tan exterior) twist around and interact with each other in a turbulent manner.
