Polar Motion Excitation and Earth's Rotation Dynamics

Earth’s polar motion refers to the gradual wandering of the planet’s rotation axis relative to its crust. This motion is driven by the redistribution of mass and angular momentum within the solid Earth, its fluid outer core, oceans, atmosphere and land hydrosphere. Secular trends over decades arise primarily from slow mantle flow and glacial isostatic adjustment, whereas interannual and decadal fluctuations are dominated by surface mass changes such as ice melt, water storage and large-scale ocean circulation. Feedbacks between core dynamics and surface processes, mediated at the core–mantle boundary, further modulate both the amplitude and phase of polar motion. Understanding these interactions is critical for the calibration of global reference frames, precise satellite navigation, climate monitoring and geophysical hazard assessment.

Research from Nature Portfolio

Recent studies have employed physics-informed machine learning to disentangle the contributions of interior and surface processes to polar motion. Ensemble neural networks trained on over a century of astronomical and space-geodetic measurements indicate that glacial isostatic adjustment and mantle convection account for the long-term drift of the rotation axis, while mass redistribution associated with ice melting and terrestrial water storage explains around ninety per cent of the observed interannual and multidecadal variability. Additional modelling reveals that torque variations at the core–mantle boundary and dynamic feedback from the fluid core both contribute to secular trends and shorter-term fluctuations. These findings place new constraints on core–mantle coupling mechanisms and refine estimates of global ice mass balance over the past century, demonstrating a two-way climate-core interaction.

Polar Motion Excitation and Earth's Rotation Dynamics publication trend

The graph below shows the total number of articles in polar motion excitation and earth's rotation dynamics across all publications each year (not limited to Nature Index journals).

Technical terms

Polar motion: The displacement of Earth’s rotation axis relative to its crust, expressed in milliarcseconds.

Effective angular momentum function: Quantitative representation of how mass redistribution and fluid circulation excite polar motion.

Chandler wobble: A free oscillation of Earth’s rotation axis with a period of approximately 433 days.

Glacial isostatic adjustment: The viscoelastic response of the mantle to the loading and unloading of ice sheets, contributing to long-term axis drift.

Earth rotation parameters (ERPs): Metrics that describe variations in length-of-day and orientation of the rotation axis used in geodesy and navigation.

References

1. Contributions of core, mantle and climatological processes to Earth’s polar motion. Nature Geoscience (2024).
2. Combination strategy for consistent final, rapid and predicted Earth rotation parameters. Journal of Geodesy (2023).
3. Evaluating Gravimetric Polar Motion Excitation Estimates from the RL06 GRACE Monthly-Mean Gravity Field Models. Remote Sensing (2020).