What do 2D PIC Simulations tell us about Magnetotail Reconnection?

Abstract:

The Magnetosphere Multiscale Mission (MMS) is designed to probe electron-scale physics during magnetic reconnection in Earth's magnetopause and magnetotail. This article will address only tail reconnection — as a non-steady-state process in which the first reconnected field lines advance away from the x-point in flux pile-up fronts directed Earthward and anti-Earthward. A microscopic physical picture of electron and ion-scale collisionless tail reconnection processes is presented based on 2-D Particle-In-Cell (PIC) simulations initiated from a Harris current sheet and on Cluster and Themis measurements of tail reconnection. Different, often subtle, signatures of diffusion regions during tail reconnection are studied. These include particle slippage, flux non-conservation and work performed on currents by electric fields. Interpretation and comparison of these signatures with each other are vital to enble spacecraft to identify reconnection events, to trigger mean­ing­ful data transfer from MMS spacecraft to Earth and to construct a useful overall physical picture of tail reconnection.