Electron vorticity indicative of the electron diffusion region of magnetic reconnection

Abstract

Abstract

While vorticity defined as the curl of the velocity has been broadly used in fluid and plasma physics, this quantity has been underutilized in space physics due to low time resolution observations. We report Magnetospheric Multiscale (MMS) observations of enhanced electron vorticity in the vicinity of the electron diffusion region of magnetic reconnection. On 11 July 2017 MMS traversed the magnetotail current sheet, observing tailward‐to‐earthward outflow reversal, current‐carrying electron jets in the direction along the electron meandering motion or out‐of‐plane direction, agyrotropic electron distribution functions, and dissipative signatures. At the edge of the electron jets, the electron vorticity increased with magnitudes greater than the electron gyrofrequency. The out‐of‐plane velocity shear along distance from the current sheet leads to the enhanced vorticity. This, in turn, contributes to the magnetic field perturbations observed by MMS. These observations indicate that electron vorticity can act as a proxy for delineating the electron diffusion region of magnetic reconnection.

Plain Language Summary

Magnetic reconnection, causing explosive magnetic energy conversion into particle energy, is one of the most fundamental physical processes occurring both within the heliosphere and throughout the universe. The multiscale kinetic structures associated with reconnection have long been a focus in space plasma physics. We investigated how electron vorticity, a physical quantity widely used in fluid physics, but underutilized in the plasma, in particular, reconnection physics, enables us to delineate multiscale kinetic boundaries of reconnection sites using the unprecedented time resolution data from National Aeronautics and Space Administration's Magnetospheric Multiscale spacecraft. The magnitude of electron vorticity to be compared with the electron gyrofrequency provides a frame‐independent indicator of the electron diffusion region, therefore, greatly advancing our ability to delineate the multiscale reconnection boundaries. This study, directly relevant to plasma/reconnection physics, will improve our understanding of fundamental physics with far‐reaching implications in astrophysics