Abstract
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.
Highlights
The notion of magnetic reconnection was originally introduced by Giovanelli (1946) to the space and astrophysical plasma physics community in order to explain violent energy releases, such as solar flares and coronal mass ejections at the Sun
We find that guide fields of up to 1 % B0 do not significantly change the obtained electron velocity distribution functions (VDFs) presented in this work
A complete set of all electron velocity distribution functions within the antiparallel reconnection site discussed in this work is available as a movie online
Summary
The notion of magnetic reconnection was originally introduced by Giovanelli (1946) to the space and astrophysical plasma physics community in order to explain violent energy releases, such as solar flares and coronal mass ejections at the Sun. We aim to associate the electron velocity distribution functions with various regions of magnetic reconnection To this end, we run a numerical experiment to generate magnetic reconnection following Geospace Environmental Modeling (GEM) (Birn et al, 2001; Pritchett, 2001) and systematically characterize the 3-D electron velocity distribution functions, in particular how the distribution functions are non-gyrotropic and where they occur. We present a comprehensive catalog of nongyrotropic electron velocity distribution functions that are relevant to magnetic reconnection Such simulation results are to be compared to Magnetospheric MultiScale (MMS) spacecraft observations from the magnetotail, similar to what was done on the dayside by Burch et al (2016a). We describe a characteristic feature of the electron diffusion region within antiparallel field reconnection Additional such catalogs for different configurations are needed for a better understanding of observed electron velocity distribution functions (VDFs)
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