Solar Wind Impact on ENAs From Earth's Subsolar Magnetosheath

As the solar wind (SW) crosses Earth's bow shock, it is heated and decelerated, resulting in a hot and dense magnetosheath ion population. This increases the probability of charge exchange between a magnetosheath proton and a geocoronal Hydrogen atom, which produces energetic neutral atoms (ENAs). These ENAs propagate away from the magnetosheath carrying information about the inherent properties of the progenitor plasma. In this work, ENA fluxes from the subsolar magnetosheath, observed by the Interstellar Boundary Explorer, are compared to SW conditions. These comparisons reveal that the passband-weighted average differential flux of ENAs is strongly influenced by the SW density, and that ENA spectra flatten with increasing SW speed and temperature, and steepen with increasing SW density. In addition, there is evidence from ENA spectra for different interplanetary magnetic field configurations that most of the ENAs observed by Interstellar Boundary Explorer come from the specularly reflected proton population in the magnetosheath.