MMS observations of large guide field symmetric reconnection between colliding reconnection jets at the center of a magnetic flux rope at the magnetopause

Abstract

We report evidence for reconnection between colliding reconnection jets in a compressed current sheet at the center of a magnetic flux rope at Earth's magnetopause. The reconnection involved nearly symmetric inflow boundary conditions with a strong guide field of two. The thin (2.5 ion‐skin depth (di) width) current sheet (at ~12 di downstream of the X line) was well resolved by MMS, which revealed large asymmetries in plasma and field structures in the exhaust. Ion perpendicular heating, electron parallel heating, and density compression occurred on one side of the exhaust, while ion parallel heating and density depression were shifted to the other side. The normal electric field and double out‐of‐plane (bifurcated) currents spanned almost the entire exhaust. These observations are in good agreement with a kinetic simulation for similar boundary conditions, demonstrating in new detail that the structure of large guide field symmetric reconnection is distinctly different from antiparallel reconnection.

Magnetospheric Multiscale Observations of an Ion Diffusion Region With Large Guide Field at the Magnetopause: Current System, Electron Heating, and Plasma Waves

“…Hence, we conclude that the bipolar structure detected at 14:16:40 UT was not caused by a vortex produced by the Kelvin‐Helmholtz instability. Another possibility is that the reconnecting current sheet was embedded in a macroscopic FTE, similar to that reported by Øieroset et al (). However, the bipolar signature in Øieroset et al () is in the magnetic field component normal to the MP, while in this case, the magnetic field rotation is in the Y GSM component, which is likely the tangential component of the MP as seen from the previous MP crossing at around 14:13 UT (see Figure ).…”

“…Another possibility is that the reconnecting current sheet was embedded in a macroscopic FTE, similar to that reported by Øieroset et al (). However, the bipolar signature in Øieroset et al () is in the magnetic field component normal to the MP, while in this case, the magnetic field rotation is in the Y GSM component, which is likely the tangential component of the MP as seen from the previous MP crossing at around 14:13 UT (see Figure ). One possible explanation for the bipolar variation in B y is that the axis of the FTE is along Z GSM instead of in the X ‐ Y plane for a typical FTE at the low latitude MP.…”

“…Another important aspect of this current sheet crossing by MMS is the parallel electron heating. While parallel electron heating has been observed in reconnection events with large guide field (Burch & Phan, ; Øieroset et al, ), the features of the parallel heating reported in this event are very different. In Burch and Phan (), T e|| exhibited two peaks in the vicinity of an EDR, with an intermediate region between the two peaks where both T e|| and current were reduced substantially (see Figure 6 of Burch & Phan, ).…”

Interaction of Magnetic Flux Ropes Via Magnetic Reconnection Observed at the Magnetopause

“…However, the coalescence of magnetic flux ropes has not been observed at the magnetopause. Most recently, Øieroset et al () found a strong ion jet within one flux rope at the magnetopause. By comparing with simulation results, they concluded that the ion jet in fact was created by reconnection occurring within the flux ropes.…”

Coalescence of magnetic flux ropes observed in the tailward high‐speed flows

“…With the Magnetospheric Multiscale Mission (MMS) data at the magnetopause, Øieroset et al . [] reported an ion jet within a large flux rope and suggested that it could be the result of the coalescence. So far, many questions on the coalescence remain, e.g., whether the coalescence can occur in the region away from the reconnection site and how long the coalescence can proceed.…”