Structure of the Current Sheet in the 11 July 2017 Electron Diffusion Region Event

Area of Science:

• Space Physics
• Plasma Physics
• Magnetospheric Physics

Background:

• Magnetic reconnection is a fundamental process in space plasmas, enabling energy transfer from the solar wind to Earth's magnetosphere.
• Electron diffusion regions (EDRs) are critical sites where magnetic reconnection occurs, involving complex electron dynamics.

Purpose of the Study:

• To examine the structure of the current sheet within an EDR during the Magnetospheric Multiscale (MMS) mission.
• To investigate the spatial variations of electron parameters and the reconnection electric field.

Main Methods:

• Analysis of MMS orbit data from the 11 July 2017 EDR event.
• Deduction of MMS location relative to the X-line to determine spatial changes in electron parameters.
• Estimation of the reconnection electric field using electron velocity gradients and nongyrotropic pressure.

Main Results:

• Observations are consistent with theoretical expectations for an inner EDR in 2D reconnection.
• The magnetic field gradient scale, dominated by electron nongyrotropic pressure, is comparable to the thermal electron gyroscale at the inner EDR edge.
• The steady-state, quasi-2D X-line approximation was valid for only ~1.4 seconds, indicating a localized inner EDR.

Conclusions:

• Electron outflow jet braking occurs within an ion inertia scale from the X-line.
• Localized processes within the EDR, and potentially outside it, significantly influence magnetotail reconnection geometry.