Synthetic Feasibility Study of Enhancing Resolution of Earth's Three‐Dimensional Interior Conductivity Using Ionospheric and Magnetospheric Sources

We develop a three‐dimensional joint inversion framework in spherical coordinate system to invert both ionospheric and magnetospheric signals from geomagnetic observatories to constrain the Earth's mantle conductivity. The methodology is built upon frequency‐mesh parallelism and multiscale tetrahedral grid finite element electromagnetic forward modeling, which enables accurate representation of the heterogeneous conductivity distribution across oceanic, terrestrial, and coastal regions. The effectiveness of this approach is validated using synthetic data sets based on a checkerboard model and a Circum‐Pacific subduction model. Experiments demonstrate that joint inversion successfully reconstructs conductivity structure at depths from 100 to 1,600 km, improving upper mantle resolution compared to using magnetospheric data only. The joint inversion effectively reconstructs most subduction zones, underscoring its effectiveness in resolving the conductivity structure of upper mantle. Applying this technique to actual geomagnetic data in the future will refine three‐dimensional models of the upper mantle and mantle transition zone, thereby offering crucial insights into deep Earth water cycling.