Observations of the change in Earth’s magnetic field—the secular variation—provide information about the motion of liquid metal within the core that is responsible for the magnetic field’s generation. High-resolution observations from the European Space Agency’s Swarm satellite mission show intense field change at high latitude, localized in a distinctive circular daisy-chain configuration centred on the north geographic pole. Here we show that this feature can be explained by a localized, non-axisymmetric, westward jet of 420 km width on the tangent cylinder, the cylinder of fluid within the core that is aligned with the rotation axis and tangent to the solid inner core. We find that the jet has increased in magnitude by a factor of three over the period 2000–2016 to about 40 km yr−1, and is now much stronger than typical large-scale flows inferred for the core. We suggest that the current accelerating phase may be part of a longer-term fluctuation of the jet causing both eastward and westward movement of magnetic features over historical periods, and may contribute to recent changes in torsional-wave activity and the rotation direction of the inner core.
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Swarm data used in the construction of the magnetic field models were provided by the European Space Agency. The support of the CHAMP mission by the German Aerospace Center (DLR) and the Federal Ministry of Education and Research is gratefully acknowledged. The staff of the geomagnetic observatories and INTERMAGNET are thanked for supplying high-quality observatory data. The deep-Earth research group within the School of Earth and Environment, University of Leeds, is thanked for comments and discussion on an early version of this manuscript. The figures were produced using the Python package Matplotlib33. The authors would like to thank R. Holme and I. Wardinski for constructive comments that helped improve the manuscript. P.W.L. was partially supported by the NERC grant NE/G014043/1.
The authors declare no competing financial interests.
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Livermore, P., Hollerbach, R. & Finlay, C. An accelerating high-latitude jet in Earth’s core. Nature Geosci 10, 62–68 (2017). https://doi.org/10.1038/ngeo2859
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