Energized Oxygen in the Magnetotail: Current Sheet Bifurcation From Speiser Motion

Abstract

AbstractOxygen can be a major constituent of magnetospheric plasma, yet the role of oxygen in the magnetosphere is not sufficiently understood. Observations of bifurcated current sheets (BCS) attributed to O have been made, yet their origin is not well understood. We examine the case of a thinning current sheet prior to the onset of magnetic reconnection using three‐species, 2.5‐D particle‐in‐cell simulations. There currently is no consensus on the formation mechanism of a BCS. Our principal result is to demonstrate that a single population of energized, Speiser orbiting, heavy ions produces a BCS. Previous particle‐in‐cell simulations have studied a three‐species system with a background of thermal O . Here we energize our O by applying an initial duskward velocity. While this is a nonphysical initialization, it does place the O into Speiser orbits streaming duskward, which has been observed in situ. Until now the connection between Speiser orbiting ions and a BCS has only been predicted. While there are two physical peaks in the current, we show that there is no splitting or bifurcation of the current in a BCS. Both current peaks are produced by a single population of ions. This is due to their gyromotion on either side of the current sheet turning them back toward the current sheet null. Additionally, there is no consensus whether magnetic reconnection is required to form a BCS or not. We confirm that magnetic reconnection is not required to produce a BCS.