Articles | Volume 35, issue 5
Regular paper
05 Sep 2017
Regular paper |  | 05 Sep 2017

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

Philippe-A. Bourdin

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.

Short summary
From computer simulations we study how free electrons behave in a region where opposite magnetic fields interact. The particles get disturbed and change their velocity and energy, similar to what happens in the tail of the magnetic field on the nightside of the Earth or during magnetic outburst events on the Sun. We provide a catalog of those particle velocities that are specific to their location within the magnetic field. Scientists may use the data for comparison with satellite observations.