New insights into an enigmatic form of magnetic reconnection

In magnetic reconnection, adjacent magnetic field lines break and snap together to form new lines. This process converts magnetic energy to both thermal energy, or heat, and kinetic energy, or the acceleration of particles, creating jets of electrons and ions. Magnetic reconnection plays a key role in many outer space events such as solar flares and auroras, as well as in laboratory methods related to nuclear fusion.

Several years ago, observations of Earth’s magnetic field by NASA’s Magnetospheric Multiscale mission led to the discovery that magnetic reconnection can occur with only electron jets, without also involving the acceleration of ions. These events also have a relatively high reconnection rate, meaning the involved magnetic field lines snap together quickly. Now Cheng‐Yu Fan and colleagues report the results of new simulations that deepen the understanding of these electron-only events.

The researchers applied a computational method known as particle-in-cell simulation to model the behavior of ions and electrons during magnetic reconnection. They ran 12 simulations to explore what factors might underlie electron-only reconnection. The results are published in Geophysical Research Letters.

The simulations revealed that the electron-only status of reconnection occurs when field lines outside of the electron diffusion region do not bend enough, leading to an underdeveloped ion diffusion region. This atypical bending happens in the early stage and may continue throughout the process if the entire system size (the size of the area in which reconnection occurs) is smaller than the radius of the path along which the ions travel.

The team also realized that magnetic reconnection and field line bending may not develop at the same pace. A relatively thin initial current sheet allows the reconnection rate to peak before field lines are fully bent, leading to calculations of high reconnection rates if they are normalized by ion parameters. However, the calculations of the reconnection rate are more typical when they are normalized by electron parameters.

These findings could help clarify the fundamental physics of magnetic reconnection, the authors suggest.

This story is republished courtesy of Eos, hosted by the American Geophysical Union. Read the original story here.