Principal component analysis of the 2010 reversal of core-surface flow beneath the Pacific Ocean

This is a pre-print, submitted for peer-review to the Journal of Studies of Earth's Deep Interior. In this paper, we investigate the behaviour of the fluid flow in the Earth's outre core throughout the 21st century. The flow of the liquid iron cocktail in the Earth's outer core generates the geomagnetic field and its rate of change, the secular variation. Assuming that magnetic diffusion is negligible on timescales shorter than 100 years, we can invert SV observations from ground observatories and geomagnetic satellites for models of the fluid flow at the top of the core. We investigate core-surface flow, modelled from observations of SV from 1997 to 2025. Historically, the core-surface flow has been predominantly westwards, as required to maintain a westward-drifting magnetic field, which is associated with a planetary gyre of westwards flow, offset from the Earth’s rotation axis. This gyre does not affect the flow in the equatorial Pacific, and we find that the flow here changes in 2010 from weakly westwards to strongly eastwards. Our model suggest that the Pacific eastwards flow has been weakening since 2020. The rise of the strong eastwards flow in the Pacific is contemporary with a change in behaviour in the inner core, as observed from geodesy and seismology, and we hypothesise that these changes in the deep interior triggered the inferred changes in flow beneath the Pacific.