Multidecadal variation of the inner core rotation
Abstract
Inner core rotation relative to the mantle is an important but as-of-yet enigmatic component of the core dynamics and core-mantle interactions. The rotation has been postulated by geodynamic studies and subsequently been supported by numerous seismic observations, which detected inner-core temporal changes over interannual to decadal scale with nearly collocated repeating earthquakes or nuclear blasts. In our recent systematic search of the inner-core temporal changes with global repeating earthquakes over the past three decades, we found that all the paths previously with significant temporal changes have now exhibited little changes over the recent decade. The consistent global pattern suggests strongly that the inner core rotates as a whole and that the rotation has paused in the recent decade under a net torque of about 1016 Nm. We further expanded the temporal coverage with analog seismic records back to the early 1960s in the College station in Alaska, for the repeating earthquakes along the South Sandwich Islands. With the extended dataset, we found that the recent pattern of the inner core rotation seems associated with a gradual turning-back as a part of a long-period (about seven decades) oscillation with another turning point in the early 1970s. The multidecadal periodicity coincides with changes in several other geophysical observations, including the length of day (LOD), magnetic field, and global climate system (mean temperature and sea level rise), pointing to a common resonating and coupling system of Earth. The inner core participates in the system probably by electromagnetic coupling with the outer core and gravitational coupling with the mantle. The angular position of the inner core from our observation is generally in phase with the reversed multidecadal LOD variations, as predicted by previous studies with the model of mantle-inner core gravitational coupling. Our observation thus provides important constraints to geodynamo models and the core-mantle coupling, and offers the first evidence for dynamic interactions between the Earth's layers from the deepest interior to the surface.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFMDI36A..02Y