Modeling sources of magnetospheric plasma during storms and substorms

It is well accepted that all of the plasma in Earth's magnetosphere derives from either the solar wind or the planet itself via the processes of ionospheric outflow. Indeed, the presence of O+ in the magnetosphere, which can only come from the ionosphere, is a clear indicator of an ionospheric source of plasma. Unlike O+ which only has one source of plasma, H+ can come from both the solar wind and the ionosphere. The solar wind H+ must enter the magnetosphere through the dayside magnetopause interactions, whereas ionospheric H+ is constantly flowing out of the ionosphere where can either be recirculated in the magnetosphere or lost down the magnetotail. In this presentation we will use merged global models combining ionospheric outflow (PWOM), multi-fluid MHD (BATS-R-US), and a ring current model (CIMI) to examine the relative importance of ionospheric and solar wind plasma in defining magnetospheric composition. We will moreover examine the pathways ions take to reach different regions of the magnetosphere and timescales required for different source populations to be effective contributors to magnetospheric composition in that region. The simulations presented consider a real event case study (2018-08-25/28) which features a large storm with comparisons to MMS observations. We also consider an idealized substorm using idealized inputs and both isotropic and anisotropic outflow conditions.