Surface core flow dynamic pressure estimation

SUMMARY The flows within Earth’s fluid outer core push and pull on the core–mantle boundary (CMB) through dynamic pressure variations, potentially leading to deformation of the CMB. It is therefore crucial to obtain a realistic estimate of the pressure associated with flows within the fluid core. In many studies, it is commonly assumed that the flow tangent to the CMB is in balance between Coriolis and pressure gradient forces, known as a tangentially geostrophic (TG) flow. A static pressure field is thereby associated kinematically to the flow field at the core’s surface. We run direct numeric simulations of the magnetohydrodynamic equations in the Boussinesq approximation that can solve for the pressure field and allow for a comparison between a fully dynamic solution and the TG pressure estimate. An excellent agreement between the two pressure fields is found for a steady image of the core surface dynamics. However, the performance of the TG pressure estimate is not without limitations. Although it effectively captures most of the temporal dynamics associated with the fluid flow, discrepancies arise, particularly near the equator and for rapid changes in flow dynamics.