Electron-only Magnetic Reconnection: Observations and Simulations*

Magnetic reconnection dissipates magnetic energy by breaking and reconnecting magnetic fields and efficiently energizes particles. Reconnection usually involves both electrons and ions. A special case of reconnection where ions did not couple to the reconnection process was discovered in the turbulent magnetosheath region downstream of Earth's quasi-parallel shock. In such events, the reconnection occurs primarily in electron-scale current sheets and are postulated to exist in turbulence where the magnetic field structures are spatially confined by the eddies generated by turbulence. In collisionless turbulence, reconnection has been suggested to drive the energy dissipation at kinetic scales and many electron-scale reconnecting current sheets are generated. The reconnection processes in these environments are limited to few ion skin depths (d_i) leading solely to the formation of the electron diffusion region (EDR), without the ion diffusion region (IDR). Hence, this type of reconnection was dubbed ‘electron-only reconnection’. Given that the scale-size of turbulent magnetic structure in the magnetosheath can be quite small, exhibiting correlation scales on the order of 1-10 d_i, electron-only reconnection may be the dominant form of reconnection in the turbulent magnetosheath and bow shock. Below ion kinetic length scales, theoretical models also suggest that electron scale reconnection may dominantly release the magnetic energy further steepening the energy spectrum.

In this talk I aim to provide the current state of electron-only reconnection starting from its discovery at the magnetosheath to the latest works in both observations and simulations.