Towards probing Earth’s upper mantle with daily magnetic field variations: exploring a physics-based parametrization of the source

Abstract The electromagnetic (EM) field variations capable of probing the electrical conductivity upper mantle and transition zone have a period range between few hours 1 day. At these periods, dominant source EM signals is ionospheric current system, which has complex spatial temporal structure. A concept global-to-local (G2L) transfer functions can handle spatially by relating global expansion coefficients with locally measured magnetic (or/and electric) fields. When estimating G2L functions, commonly expanded into spherical harmonics (SH). In this paper, we explore an alternative parametrization based on principal component analysis (PCA) Fourier transformed output from physics-based Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM). Specifically, investigate whether fields computed in realistic three-dimensional model Earth excited PCA-based agree better observatory data than those same but induced SH-based source. Using PCA to capture compared SH parametrization, find that agreement during magnetically disturbed times at shorter periods. Vice versa, it poorer quiet longer