Physically constrained empirical modelling of climatological F-region magnetic field and electric current variations

The Earth’s ionosphere hosts a complex electric current system that generates magnetic fields. The study of these electric currents and fields provides crucial insights into the ionosphere-thermosphere system, lower atmospheric dynamics, magnetospheric physics, and ionospheric plasma distribution and dynamics.

A particularly valuable dataset to study these currents and fields comes from magnetic measurements acquired by low Earth orbit (LEO) satellites. Some of these satellites provide high-accuracy vector magnetic data that are calibrated using onboard independent scalar measurements. This is the case for the ESA Earth Explorer Swarm satellite constellation, the CHAMP satellite, or the more recently launched MSS-1 satellite. Other satellites, such as the GRACE, GRACE-FO, CryoSat-2, and GOCE satellites, provide complementary, less-accurate platform magnetic vector data, which help improve the overall space-time satellite data coverage. Data from all these satellites are already used to recover and study the signals from the Earth’s outer core, the lithosphere, the oceans, the magnetospheric and the E-region ionospheric currents, as well as the currents induced in the solid Earth by these time-varying ionospheric and magnetospheric fields.

Since LEO satellites orbit within the ionospheric F region, they also provide valuable in situ measurements of F-region ionospheric magnetic fields and electric currents. Interpreting the highly dynamic and spatially complex F-region signals in data from satellites at different altitudes and with very different geographic and local time coverage, however, is a challenging problem. A traditional approach in geomagnetism is to construct empirical models to extract and synthesize signals of interest from multiple data sources. Applied to F-region ionospheric fields and currents, it generally leads to strongly underdetermined inverse problems that can hardly be solved robustly due to incomplete satellite data coverage, even with modern satellite data. Recent research has nevertheless demonstrated that additional progress could be made by relying on optimized spatial basis functions using numerical simulations from realistic physics-based models, such as the Thermosphere-Ionosphere-Electrodynamics General Circulation Model. Such an approach has many advantages, including the ability to fill gaps at altitudes where no satellite data are available and to improve model numerical stability.

We will present our first very encouraging attempt to build a climatological model of F-region magnetic fields and ionospheric currents based on such an approach. Possible avenues for future improvements will also be discussed.