Electron Distribution Functions Around a Reconnection X‐Line Resolved by the FOTE Method. Issue 3 (14th February 2019)

• Record Type: Journal Article
• Authors: Wang, Z.; Fu, H. S.; Liu, C. M.; Liu, Y. Y.; Cozzani, G.; Giles, B. L.; Hwang, K.‐J.; Burch, J. L.
• Is Part Of: Geophysical research letters. Volume 46:Issue 3(2019)
• Page Start: 1195
• Page End: 1204
• Publication Date: 2019-02-14
• Subjects: magnetic reconnection -- electron distribution functions -- magnetic topology -- FOTE method -- reconstruction; Geophysics -- Periodicals; Planets -- Periodicals; Lunar geology -- Periodicals; 550
• DOI: 10.1029/2018GL081708
• Languages: English
• ISSNs: 0094-8276

Abstract

Abstract: Using data from the MMS mission and the First‐Order Taylor Expansion (FOTE) method, here we reveal electron distribution functions around a reconnection X‐line at the Earth's magnetopause. We find cigar distribution of electrons in both the magnetosphere‐side and magnetosheath‐side inflow regions, isotropic distribution of electrons at the separatrix, and loss of high‐energy electrons in the antiparallel direction in the magnetosheath‐side inflow region. We interpret the formation of cigar distribution in the inflow regions using the Fermi mechanism—as suggested in previous simulations, the loss of high‐energy electrons in the magnetosheath side using the parallel electric fields—which evacuate electrons to escape the diffusion region along the antiparallel direction, and the isotropic distribution at the separatrix using the pitch angle scattering by whistler waves—which exist frequently at the separatrix. We also find that the electron distribution functions can change rapidly (within 60 ms) from isotropic to cigar as the spacecraft moves slightly away from the separatrix. Plain Language Summary: Magnetic reconnection is a key process responsible for many explosive phenomena in nature such as solar flares and magnetospheric substorms. Up to now, the electron behaviors (particularly electron distribution functions) around the reconnection X‐line have not been well revealed, because the X‐line topology is unavailable in previous study. Using data from the MMS mission and the newly developed FOTE method, here we investigate electron distribution functions around a reconnection X‐line and explain the formation mechanisms of these distributions successfully. Key Points: For the first time, we reveal electron distributions around a reconnection X‐line using the FOTE method, rather than cartoons or simulations We find different types of electron distributions around the X‐line, and explain the formation mechanisms of these distributions successfully We find a rapid change of electron distribution within 60 ms. Such rapid change can only be revealed by FOTE but not other methods