An empirical 3D model of the ionospheric currents spanning 20 years

Abstract:

State-of-the-art numerical simulations of ionospheric electrodynamics are capable of capturing the dominant spatial patterns of the primary current systems, including the equatorial and auroral electrojets, Sq, gravity, pressure-gradient, and field-aligned currents. However, these simulations often provide poor predictions of observations recorded by magnetic instrumentation on ground and in space, due in part to the complex variability associated with the neutral wind and high-latitude forcing mechanisms. Physics-based simulations also have difficulty in modeling spatial structure associated with different periods of the source signals. Purely empirical models of the ionospheric currents are typically limited to 2D equivalent ionospheric sheet current flow, due to the large number of model parameters needed to constrain the sparse set of available magnetic observations, and so they provide little to no information on 3D structures in the currents. In this study, we develop a hybrid approach, combining physics-based simulations with a dataset of ground and space observations, in order to build a time-dependent model of the ionospheric currents with fully 3D spatial structure. We apply principal components analysis (PCA) to the outputs of the TIEGCM to construct a set of spatial modes representing the dominant sources of variability in the ionospheric current. A similar approach is applied to the ground observatory network to construct temporal modes which capture time variations of the ionosphere in a range of frequency bands. Finally, these spatio-temporal modes are fitted to a large database of satellite and ground observations from 2000-2020 to build a fully 3D model of the ionospheric currents spanning nearly two solar cycles.