Ionospheric outflow supplies nearly all of the heavy ions observed within the magnetosphere, as well as a significant fraction of the proton density. While much is known about upflow and outflow energization processes, the full global pattern of outflow and its evolution is only known statistically or through numerical modeling. Because of the dominant role of heavy ions in several key physical processes, this unknown nature of the full outflow pattern leads to significant uncertainty in understanding geospace dynamics, especially surrounding storm intervals. That is, global models risk not accurately reproducing the main features of intense space storms because the amount of ionospheric outflow is poorly specified and thus magnetospheric composition and mass loading could be ill-defined. This study defines a potential mission to observe ionospheric outflow from several platforms, allowing for a reasonable and sufficient reconstruction of the full outflow pattern on an orbital cadence. An observing system simulation experiment is conducted, revealing that four well-placed satellites are sufficient for reasonably accurate outflow reconstructions. The science scope of this mission could include the following: reveal the global structure of ionospheric outflow; relate outflow patterns to geomagnetic activity level; and determine the spatial and temporal nature of outflow composition. The science objectives could be focused to be achieved with minimal instrumentation (only a low-energy ion spectrometer to obtain outflow reconstructions) or with a larger scientific scope by including contextual instrumentation. Note that the upcoming Geospace Dynamics Constellation mission will observe upwelling but not ionospheric outflow.

Oxygen ions are a major constituent of magnetospheric plasma, yet the role of oxygen in processes such as magnetic reconnection is poorly understood. Observations show that significant energized $O^+$ can be present in a magnetotail current sheet. A population of thermal $O^+$ only has a minor effect on magnetic reconnection. Despite this, published studies have so far only concentrated on the role of the low-energy thermal $O^+$. We present a study of magnetic reconnection in a thinning current sheet with energized $O^+$ present. Well-established, three-species, 2.5D Particle-In-Cell (PIC) kinetic simulations are used. Simulations of thermal $H^+$ and thermal $O^+$ validate our setup. We energize a thermal background $O^+$ based on published measurements. We apply a range of energization to the background $O^+$. We discuss the effects of energized $O^+$ on current sheet thinning and the onset and evolution of magnetic reconnection. Energized $O^+$ has a major impact on the onset and evolution of magnetic reconnection. Energized $O^+$ causes a two-regime onset response in a thinning current sheet. As energization increases in the lower-regime, reconnection develops at a single primary {X}-line, increases time-to-onset, and suppresses the rate of evolution. As energization continues to increase in the higher-regimes, reconnection develops at multiple {X}-lines, forming a stochastic plasmoid chain; decreases time-to-onset; and enhances evolution via a plasmoid instability. Energized $O^+$ drives a depletion of the background $H^+$ around the current sheet. As energization increases, the thinning begins to slow and eventually reverses, leading to disruption of the current sheet via a plasmoid instability.

Oxygen ions can be a major constituent of magnetospheric plasma, yet the role of oxygen in the magnetosphere is often not sufficiently understood. We examine the case of a thinning current sheet prior to the onset of magnetic reconnection. We perform 2.5D PIC simulations of a 3-species system of electrons, protons and heavy ions ($O^+$). We initiated the simulations using the well-known GEM Challenge configuration. Our approach differs from previous simulations involving heavy ions in two important aspects. First, we initiate the simulations with energized $O^+$ as opposed to using a thermal population. The energization is based on published in-situ measurements consisting of an initial dusk-ward velocity equivalent to $\sim$7 KeV. Second, we tracked the particles directly in the simulation rather than performing test particle tracing in post processing. We show three main results. First, energized dawn-dusk streaming ions exhibit sustained Speiser motion. Second, a single population of heavy ions can produce a stable bifurcated current sheet. Third, magnetic reconnection is not required to produce a bifurcated current sheet.