Filling in the global MHD model gap region: Enabling predictions of magnetic field perturbations at Low-Earth Orbit

Field‐aligned currents (FACs) mediate magnetosphere-ionosphere coupling and can strongly enhance the electromagnetic energy input into the upper atmosphere during space‐weather disturbances. Space-based magnetometers in low-Earth orbit (LEO) have been used for decades to infer local FACs. However, the magnetic field perturbations they measure often contain additional contributions from magnetospheric, ionospheric, and ground-induced currents. Isolating these contributions using single or dual spacecraft remains challenging, instead requiring local spacecraft constellations (e.g., Swarm or the GDC mission concept) and motivating physics-based tools to disentangle their signatures.
Global magnetohydrodynamic (MHD) simulations of the coupled magnetosphere-ionosphere system offer a potential framework for assessing the different current-system’s contributions and for enabling direct comparisons with in-situ data. However, numerical constraints introduce a several-Earth-radii “gap region” between the ionosphere and inner magnetosphere, preventing direct prediction of magnetic fields at LEO.
We extend existing methods traditionally used to compute ground magnetic perturbations so that they operate at LEO and use them as a benchmark to evaluate alternative approaches that are more efficient and stable than traditional full three-dimensional Biot-Savart integration. We validate the methods by implementing them in the Gorgon global MHD model.
We present results on the magnetic field contributions from the different current systems at LEO and discuss implications for current and future low-orbit missions (TRACERS, AMPERE, and emerging megaconstellations), as well as for advancing next-generation space-weather forecasting capabilities to LEO.