Working towards the goal of understanding solar wind entry to the Earth’s magnetosphere, this study examines solar-origin ion composition in the magnetotail. During its trajectory, Wind spent a significant amount of time in the Earth’s magnetotail, where its SupraThermal Ion Composition Spectrometer (STICS) measured the mass and mass per charge of protons, alpha particles, and heavy ions with an energy/charge ratio up to 226 keV/e. For this reason, STICS measurements within the magnetosphere from 1995 to 2002 help us identify preferential entry between the different solar wind ion species. This study statistically analyzes how the density ratio between solar wind heavy ions and alpha particles ([O6+ + C5+ + Fe10+] / He2+) varies for different upstream conditions and locations within the magnetosphere: Interplanetary Magnetic Field (IMF) orientation, low vs. high solar wind density (NSW), low vs. high solar wind dynamic pressure (PDyn), slow vs. fast solar wind (VSW), and dawn vs. dusk. Our results indicate that the solar wind heavies enter the magnetosphere more efficiently than He2+ during northward IMF and high NSW. In addition, these ratios exhibit a dawn-dusk asymmetry, highly skewed towards the dawn side for most upstream cases likely due to charge-exchange processes.

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.