Reconstruction of the Electron Diffusion Region of Magnetotail Reconnection Seen by the MMS Spacecraft on 11 July 2017

• Published in: Journal of geophysical research. Space physics 2019-01, Vol.124 (1), p.122-138
• Main Authors: Hasegawa, H., Denton, R. E., Nakamura, R., Genestreti, K. J., Nakamura, T. K. M., Hwang, K.‐J., Phan, T. D., Torbert, R. B., Burch, J. L., Giles, B. L., Gershman, D. J., Russell, C. T., Strangeway, R. J., Lindqvist, P.‐A., Khotyaintsev, Y. V., Ergun, R. E., Kitamura, N., Saito, Y.
• Format: Article
• Language: English
• Subjects: Aeronautics; Aerospace environments; Brightening; Broadband; Charged particles; Diffusion; Electric currents; Electric fields; Electromagnetic fields; Electron diffusion; electron diffusion region; Electrons; Electrostatic waves; Energy conversion; Energy dissipation; Flow pattern; Fluid dynamics; Fluid flow; Frequency ranges; Magnetic fields; Magnetic reconnection; Magnetohydrodynamic equations; Magnetohydrodynamics; Magnetospheric Multiscale; Magnetospheric-solar wind relationships; magnetotail; Magnetotail reconnection; Magnetotails; Planetary magnetospheres; reconnection rate; Reconstruction; Solar energy; Solar flares; Solar wind; Spacecraft; Spatial resolution; Stagnation point; Wind power
• ISSN: 2169-9380; 2169-9402; 2169-9402
• DOI: 10.1029/2018JA026051

We present results from the reconstruction of the electron diffusion region of magnetotail reconnection observed by the Magnetospheric Multiscale (MMS) spacecraft on 11 July 2017. In the event, the conditions were suited for the reconstruction technique, developed by Sonnerup et al. (2016, https://doi.org/10.1002/2016JA022430), that produces magnetic field and electron streamline maps based on a two‐dimensional, time‐independent, inertialess form of electron magnetohydrodynamic equation, assuming an approximately symmetric current sheet and negligible guide magnetic field. For such a two‐dimensional and steady structure, the X line orientation can be estimated from a method based on Ampère's law using single‐spacecraft measurements of the magnetic field and electric current density. Our reconstruction results indicate that although the X point was not captured inside its tetrahedron, MMS approached the X point as close as one electron inertial length ~27 km. The opening angle of the recovered separatrix field line, combined with theory, suggests that the dimensionless reconnection rate was 0.17, which is consistent with the measured reconnection electric field 2–4 mV/m. The stagnation point of the reconstructed electron flow is shifted earthward of the X point by ~90 km, one possible interpretation of which is discussed. The energy conversion rate j · E′ in the electron frame tends to be higher near the stagnation point, consistent with earlier observations and simulations, and is not correlated with the amplitude of broadband electrostatic waves observed in the upper‐hybrid frequency range. The latter suggests that the waves did not contribute to energy dissipation in this particular electron diffusion region. Plain Language Summary Magnetic reconnection is a fundamental plasma process that controls transfer of solar wind energy and mass to planetary magnetospheres and causes explosive energy release associated with solar flares and sudden auroral brightening. National Aeronautics and Space Administration's Magnetospheric Multiscale (MMS) mission, which consists of four identical spacecraft launched in March 2015, aims at elucidating how magnetic reconnection works with unprecedented high temporal and spatial resolution measurements of charged particles and electromagnetic fields in space. MMS has been observing the Earth's magnetotail since May 2017 and encountered the central region of magnetic reconnection, called the electron diffusion region, on 11 J