Current Continuity in Auroral System Science: Data-Driven Auroral GEMINI Simulations

Auroral arc scale M-I coupling involves complex system level science and is an open area of study (Wolf, 1975; Seyler, 1990; Cowley, 2000; Marghitu, 2012; Clayton et al., 2021; Wang et al., 2024). The ionosphere plays a non-passive role in this coupling by keeping the closure of field-aligned currents (FAC) self-consistent with both plasma convection and the conductivity volume imparted by accelerated auroral precipitation.

The current continuity equation (Eq. 8.15 in Kelley (2009)) tells us that, with a horizontal map of FAC (or ExB flow) and with knowledge of the ionosphere's conductances, a solution can be found for the plasma flow (or FAC). However, this integrates out all altitudinal dependencies. Pedersen closure currents peak at higher altitudes than Hall currents which, other than morphological, also has energetic implications as only Pedersen currents dissipate electromagnetic energy (Kaeppler, 2011). Altitude dependent, finite recombination times, together with plasma transport, can produce 3D electron density structures providing an auroral precipitation hysteresis in conductance maps. Moreover, the 3D conductivity volume is highly sensitive to auroral precipitation by means of impact ionization, in part due to altitude dependent ionization rates (Fang et al., 2008, 2010). Though current continuity is well understood for sheetlike aurorae, this accelerated precipitation often has significant spatiotemporal as well as spectral structure, directly impacting the 3D conductivity volume.

We investigate several data-driven 3D auroral simulations provided by the GEMINI model (Zettergren et al., 2015). This is a state-of-the-art, multi-fluid, quasi-electrostatic model driven with topside maps of parallel potential drop (used with accelerated precipitation spectra), total precipitation energy flux, and ExB flow. Maps of precipitation energetics are inverted from multi-spectral imagery. To generate the flow maps, we use conjunctions of multi-spectral, all-sky auroral imagery and data tracks of plasma flow (radars, spacecraft, and/or rockets) with a process called "replication" (van Irsel et al. 2024). With this, aside from gaining abundant 3D information on auroral system science, our aim is to reduce these data-driven simulations input maps to a manageable set of auroral feature parameters (arc width, FAC amplitude, etc.) that can create idealized simulations. Such simulations can be used for a series of interesting sensitivity tests.