Reconstruction of the electron diffusion region observed by the Magnetospheric Multiscale spacecraft: First results

• Published in: Geophysical research letters 2017-05, Vol.44 (10), p.4566-4574
• Main Authors: Hasegawa, H., Sonnerup, B. U. Ö., Denton, R. E., Phan, T.‐D., Nakamura, T. K. M., Giles, B. L., Gershman, D. J., Dorelli, J. C., Burch, J. L., Torbert, R. B., Russell, C. T., Strangeway, R. J., Lindqvist, P.‐A., Khotyaintsev, Y. V., Ergun, R. E., Cassak, P. A., Kitamura, N., Saito, Y.
• Format: Article
• Language: English
• Subjects: Climatology; Data analysis; Data processing; Diffusion; Distance; Dye dispersion; Earth; Earth magnetosphere; Electric field; Electric fields; Electron diffusion; electron diffusion region; electron magnetohydrodynamics; Electron-magnetohydrodynamics equations; Electrons; Energy dissipation; Energy exchange; Fields; Fluid dynamics; Geomagnetic storms; Geomagnetism; Hall physics; Identification; Inflow; Magnetic field; Magnetic field configurations; Magnetic fields; Magnetic reconnection; Magnetic reconnections; Magnetic storms; Magnetism; Magnetohydrodynamics; Magnetopause; Magnetopause reconnection; Magnetosphere; Magnetospheres; Magnetospheric multi scale; Mass; Mathematical models; Methods; Outflow; Reconstruction; Resolution; Signatures; Solar energy; Solar wind; Space weather; Spacecraft; Storms; Structures; Three-dimensional structure; Time dependence; Velocity; Weather; Wind power generation
• ISSN: 0094-8276; 1944-8007; 1944-8007
• DOI: 10.1002/2017GL073163

We present first results of the reconstruction of the electron diffusion region (EDR) based on a two‐dimensional, incompressible, and inertialess version of the electron magnetohydrodynamics equations. The method is applied to 30 ms resolution magnetic field, and electron moments data taken when the Magnetospheric Multiscale (MMS) spacecraft observed an EDR of near‐antiparallel magnetopause reconnection on 16 October 2015. An X‐type magnetic field configuration and quadrupolar Hall fields, consistent with the electron inflow and outflow, are successfully recovered. While MMS encountered a region of significant energy dissipation on the magnetospheric side of the sub‐ion‐scale current sheet, the reconstructions show that the MMS tetrahedron missed the X line by a distance of a few kilometers (~2 electron inertial lengths). The estimated reconnection electric field is 0.42–0.98 mV/m, equivalent to the dimensionless reconnection rate of 0.11–0.25. Signatures of three‐dimensional structures and/or time‐dependent processes are also identified. Plain Language Summary Magnetic reconnection that often occurs at the outer boundary of Earth's magnetosphere plays a central role in transporting mass and energy of solar wind into the near‐Earth space and thus forms the basis of most space weather phenomena, including aurora and geomagnetic storms. However, we still do not fully understand how and how efficiently this process works. We present a two‐dimensional image of the magnetic reconnection region reconstructed for the first time from a new data analysis tool by use of high time resolution (30 ms) magnetic field and plasma measurements made by the four‐spacecraft Magnetospheric Multiscale (MMS) mission launched in March 2015. The magnetic field configuration and electron velocity field pattern recovered from the tool are consistent with fast magnetic reconnection. But the results show that the MMS spacecraft in fact missed the very site of the reconnection by a distance of a few kilometers (~2 electron inertial lengths) in the event on 16 October 2015 reported by Burch et al. (2016). The results also demonstrate that the new tool is powerful in revealing the structure and fundamental processes of magnetic reconnection in space on the basis of in situ observations. Key Points First results from electron MHD‐based reconstruction of the electron diffusion region of magnetopause reconnection seen by MMS The X point was likely within a few kilometers of the MMS4 spacecr