Assessing the Relative Impact of Distinct Ionospheric Outflow Populations on Geospace Dynamics using Multi-Fluid Global MHD simulations

Abstract:

Satellite observations and numerical modeling studies have demonstrated that ionospheric ion outflows of different species, source locations and energies populate and interact with distinct regions of the magnetosphere, and therefore can have profoundly different impacts on the coupled solar wind-magnetosphere-ionosphere (SWMI) system. In previous modeling studies, multi-fluid global simulations of the SWMI interaction typically use one fluid to model the solar wind and a second fluid to represent the outflowing ions. These studies are limited as they are incapable of tracking multiple, distinct ionosphere-sourced ion populations. Either significant ion populations and their influence must be excluded from the simulation or multiple ion populations must be combined into a single fluid.

In this study, a multi-fluid adaption of the Lyon-Fedder-Mobarry (MFLFM) model that is capable of including numerous separate fluids is used to: (1) evaluate how different outflowing ion populations propagate in the magnetosphere and enter the tail, (2) determine their resulting magnetospheric distribution, and (3) calculate their relative impacts on SWMI coupling. The outflow flux for each population is regulated using causally driven models based on empirical data. These models include specifications for transversely accelerated O+ originating from the cusp and nightside auroral region, H+ polar wind outflow and the plasmasphere. The outflow distributions and hemispheric outflow flux resulting from these models, and their resulting composition in the magnetosphere are validated using satellite data. The effects of each individual ion source on dayside reconnection, electrodynamic magnetosphere-ionosphere coupling and magnetotail processes are evaluated. Among other effects, we find that ionospheric ions that are entrained directly into the warm plasma cloak are more effective at reducing the dayside reconnection potential than ions that are transported further downtail and are convected Earthwards in the plasma sheet.