Auroral System Science - Determining Geophysical Boundary Conditions for Multifluid Volumetric Simulations of Auroral Arcs

Auroral complexity exists even for basic sheetlike auroral arcs with minimal longitudinal gradients. We're simulating such arcs in 3D using state-of-the-art ionospheric modelling (GEMINI, Zettergren et al., 2015). So far, this has introduced two major hurdles which require careful thought: 1) How do we choose self-consistent, geophysical model drivers, and 2) how do we visualize and interpret the resulting exceptionally rich data volumes.

The topside forcing of our model space requires time-dependent, 2D maps of precipitation energy, energy flux, and of current OR flow. These maps are generated by defining across-arc cuts that are replicated along a predefined arc contour (Clayton et al. 2021) typically based on imagery. We develop these maps to be parameterized cartoons, as opposed to explicitly data-driven maps, such that they can be systematically varied and compared. This comes with the trade-off that requires ensuring these maps remain self-consistent and geophysical. To address this we can: 1) use literature statistics (Wu, 2020) in determining parameters, 2) use featurized parameters drawn from current, flow, and imagery data (SWARM, THEMIS-GBO) in determining relative typical morphologies, and 3) incorporate theory in relating current to flow to precipitation. Examples of the latter include the use of the Knight relation (Knight, 1973), matching the ratio of the electric and magnetic field perturbations appropriately to the simulation's average Pedersen/Alfvén conductance, and improving the model's impact ionization scheme to better match non-Maxwellian, inverted-V precipitation.

We'll use a catalogue of simulations to investigate these methods and figure out the impact of different choices. Example comparisons include deliberately (mis)matched field-aligned current and precipitation maps, simulations with precipitation current provided by the Knight relation versus ones that only include magnetospheric current, and simulations with (non-)Maxwellian precipitation. To assess geophysicality, we aim to investigate Poynting flux and Joule heating. Ultimately, this work can provide the community with a basic starting point in simulating auroral arcs from which less idealized, non-sheetlike arcs can be explored.