Unusual fluctuations in diverse surface measurements hint at periodic movements within the Earth's iiner core. Geoscientists Yachong An and Hao Ding from Wuhan University discovered an 8.5-year periodic wobbling in the inner core while examining subtle changes in Earth's day length and pole motion.
Earth's Inner Core Wobble Ever 8.5 Years
The Earth is composed of four layers: the crust, mantle, outer core, and inner core. The conventional understanding of Earth's rotation has been rooted in the assumption of a uniform density distribution in the mantle and core, extending radially from the center outward. This presumption implies that the rotation axis of Earth's core aligns with that of the mantle.
However, Dr. Ding challenged this traditional perspective by pointing out that the results of Earth's free oscillation, or its natural overall oscillations, indicate highly heterogeneous density structures within Earth's interior. This challenges the realistic nature of the uniform density assumption.
In 2018, Professor Ding's analysis of Earth's polar motion (PM) revealed an unexpected signal with an approximately 8.5-year period, suggesting the existence of an Inner Core Wobble (ICW). This surprising finding gained further support from a similar signal observed in the changes in the length of day (ΔLOD) of Earth's rotation, leading to a significant shift in our understanding.
Expanding on these discoveries, researchers carefully examined the PM and ΔLOD of Earth's rotation, identifying the approximately 8.5-year signal in PM as the manifestation of ICW. This signal consistently appeared in the periodic movement of Earth's rotational axis, or ΔLOD.
By excluding external excitation sources like atmospheric, oceanic, and hydrological influences, the study suggests a profound connection between ICW and Earth's rotational dynamics.
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Implications of a Wobbling Inner Core
The Chinese researchers officially affirmed the existence of ICW and disclosed a fixed 0.17-degree tilt between Earth's inner core and mantle, challenging conventional beliefs and providing crucial insights into Earth's internal dynamics and density distribution.
The findings detailed in the study, titled "Inner core static tilt inferred from intradecadal oscillation in the Earth's rotation" published in Nature Communications, suggests a potential eastward differential rotation angle of the inner core and misalignment in the symmetry axes of the lower mantle/core-mantle boundary layer with the upper mantle.
Dr. Ding explained that these deviations provide valuable constraints for the 3D density model of the mantle and challenge assumptions in traditional theories, particularly those related to the liquidity-core oblate.
The identified ~8.5-year periodicity of the ICW reveals a density jump of about 0.52 g/cm3 at the inner core boundary, indicating a discernible change in density at this crucial boundary.
While the focus of the research is on the inner core, the study suggests that the static tilt and ICW may have broader implications for geophysical phenomena. Dr. Ding noted that the static tilt could induce changes in the shape of the liquid core, affecting fluid motion and potentially influencing the geomagnetic field.
This discovery challenges traditional assumptions about Earth's rotation and provides insights into the intricacies of the planet's interior dynamics. Future research aims to explore the stratified structure and density of Earth's core, seeking clarity on the coexistence of different conceptual theories.
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