The Importance of Self-Consistent Conductivity in Coupling Magnetosphere-Ionosphere-Thermosphere Models

The high-latitude ionosphere is a dynamic environment influenced not only by magnetospheric precipitation and currents from above but thermospheric motions such as waves, tides, and neutral upwelling from below. All of these external physical processes, as well as the ion production, loss and transport from within, act together to determine the ionospheric state (viz. local density, momentum, and temperature). As a consequence, it is common practice to treat the ionosphere as the "end-of-the-road" in a coupled Magnetosphere-Ionosphere-Thermosphere (MIT) model. Realistically, the ionosphere plays a critical role in determining the local conductivity, which directly impacts how magnetospheric currents are closed through the high-latitude ionosphere. This ionospheric feedback/influence is crucial for an accurate description of the MIT system.

For this study, the Space Weather Modeling Framework (SWMF) is used to couple the Ridley Serial (RS) model of ionospheric electrodynamics to the Global Ionosphere/Thermosphere Model (GITM). With traditional one-way coupling, RS receives magnetospheric field aligned currents (FACs) and precipitation from the SWMF, calculates the Pedersen and Hall conductance from the precipitation via the Robinson formula, and combines the FACs and conductances to obtain the electric potential. This potential is passed back to the SWMF and onwards, with the auroral precipitation, to GITM to drive ionospheric dynamics. In contrast, utilizing two-way coupling, the conductances are calculated in GITM (from the local ion and neutral densities) and passed to RS. This bypasses the need to use the Robinson formula and directly takes into consideration the impacts of ionospheric dynamics. The result of this new approach is the inclusion of a conductance value that is dynamic, first-principles-based, and self-consistent with magnetosphere-ionosphere-thermosphere interactions. Consequences of one-way and two-way coupling are discussed in detail and comparisons presented that illustrate the importance of self-consistently including ionospheric conductivity, as calculated by GITM, for idealized and realistic IMF conditions.