Magnetic field reconnection is one of the most efficient and important mechanisms for magnetic energy being converted to other forms of energy. It is widely accepted that magnetic field reconnection plays a key role in various eruptive phenomena in solar atmosphere and planetary magnetospheres. The reconnection rate controls the energy release process, and therefore has been studied for decades through observations and simulations.
Nakamura et al.  push these studies a step forward by investigating the event on 11 July 2017, which was the first observed electron diffusion region in the magnetotail by the Magnetospheric Multiscale mission. By combining the results from observational analysis and kinetic simulations, the authors reliably obtained that the normalized reconnection rate is about 0.15–0.2, corresponding to an unnormalized reconnection rate of 2–3 mV/m. The results show strong evidence that the reconnection rate has a close relationship with the amplitudes of geomagnetic disturbances.
Citation: Nakamura, T. K. M., Genestreti, K. J., Liu, Y.‐H., Nakamura, R., Teh, W.‐L., Hasegawa, H., et al. . Measurement of the magnetic reconnection rate in the Earth’s magnetotail. Journal of Geophysical Research: Space Physics, 123. https://doi.org/10.1029/2018JA025713
—Yuming Wang, Editor, JGR: Space Physics