Flux Transfer Event With an Electron‐Scale Substructure Observed by the Magnetospheric Multiscale Mission

Abstract

On 12 November 2015 the Magnetospheric Multiscale (MMS) spacecraft traversed the magnetopause from the magnetosphere to the magnetosheath encountering evidence of magnetic reconnection and a tiny flux transfer event (FTE) on the magnetosheath side of the magnetopause boundary layer. The FTE exhibited a large negative-positive bipolar variation in the normal magnetic field component (B N), an enhanced (negative) north-south component direction (B L), and a variation in the third component B M resembling a "W" shape with negative values close to the edges and positive values near the center. Using the tetrahedron formation, we estimate that the FTE moved southward and duskward with a speed of V FTE = 324 km/s. The FTE size in the transverse direction is 518 km, which corresponds to 4.42 ion gyroradii. We identify an internal layer where the electron bulk flow velocity exhibits different behaviors at each of the four spacecraft and the current density was more intense at two spacecraft. Within the FTE's core region, the ion bulk flow behavior was similar for all four spacecraft. Using the velocity obtained from timing analysis, we estimate a dimension of this core region to be 181.4 km, which corresponds to 1.5 ion gyroradii. It is evident that the internal region is not large enough to affect the ion behavior but can do so for electrons. We conclude that the FTE's core is an electron-scale substructure.

Small-scale Field-aligned Currents in the Magnetopause Boundary Layer

“…Considering that FTEs near the magnetopause are often considered as the products of magnetic reconnection, the possibility of generating FACs in FTEs is significant. Silveira et al (2020) observed strong FAC features in the FTEs. Additionally, some studies utilized a quasistatic magnetosphere-ionosphere coupling model driven by a vortex in the boundary layer to determine how FACs depend on ionospheric and boundary layer parameters (e.g., Johnson et al 2021).…”

Magnetospheric Reconnection and Geomagnetic Storms: A Personal Perspective

“…Due to the available in-situ plasma and magnetic field observations at the central/diffusion region of magnetospheric reconnection, obtained more recently with dedicated satellite missions (such as THEMIS and MMS), I had the opportunity to participate in some related studies (Koga et al, 2014(Koga et al, , 2019Lu et al, 2020;Silveira et al, 2020;Souza et al, 2017;Wang et al, 2017) and to also join (as a co-investigator) a research project of the Chinese Academy of Sciences with the aim of launching a multiscale mission to study Magnetospheric Reconnection on its micro and macro scales, using a central satellite and 12 associated cubesats (Dai et al, 2020). With such a mission one expects to observe reconnection parameters simultaneously at the central-diffusion region of reconnection as well as at several external locations of its macro domains.…”