Catalog of fine-structured electron velocity distribution functions $-$ Part 1: Antiparallel magnetic-field reconnection (Geospace Environmental Modeling case)

TL;DR

This paper analyzes electron velocity distribution functions in antiparallel magnetic reconnection using high-resolution PIC simulations, aiming to create a detailed catalog for comparison with MMS observations.

Contribution

It introduces a refined method for identifying electron diffusion regions and provides detailed electron VDFs across reconnection sites, advancing understanding of reconnection physics.

Findings

Regions with strong non-gyrotropy identified near the separatrix

Refined criterion for electron diffusion region detection

Gradual variation of electron VDFs depending on location

Abstract

To understand the essential physics needed to reproduce magnetic reconnection events in 2.5-D particle-in-cell (PIC) simulations, we revisit the Geospace Environmental Modeling (GEM) setup. We set up a 2-D Harris current sheet (that also specifies the initial conditions) to evolve the reconnection of antiparallel magnetic fields. In contrast to the GEM setup, we use a much smaller initial perturbation to trigger the reconnection and evolve it more self-consistently. From PIC simulation data with high-quality particle statistics we study a symmetric reconnection site, including separatrix layers, as well as the inflow and the outflow regions. The velocity distribution functions (VDFs) of electrons have a fine structure and vary strongly depending on their location within the reconnection setup. The goal is to start cataloging multidimensional fine-structured electron velocity distributions showing different reconnection processes in the Earth's magnetotail under various conditions. This will enable a direct comparison with observations from, e.g., the NASA Magnetospheric MultiScale (MMS) mission, to identify reconnection-related events. We find regions with strong non-gyrotropy also near the separatrix layer and provide a refined criterion to identify an electron diffusion region in the magnetotail. The good statistical significance of this work for relatively small analysis areas reveals the gradual changes within the fine structure of electron VDFs depending on their sampling site.