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Cooling patterns of Earth's core explains peculiarities in magnetic fields


Numerical simulations by LIFD geophysicists explain how convection in the Earth's mantle affects it's magnetic field. The mantle influences the magnetic field by imposing a pattern of cooling that controls the dynamics of fluid flow at the top of the outer core.

Thermal interactions between Earth’s core and mantle provide the power that maintains the geomagnetic field. However, the effect of these interactions on magnetic field behaviour remains uncertain. LIFD researchers Prof. Jon Mound, and Prof. Christopher Davies, from the School of Earth and Environment, have published numerical dynamo simulations in the scientific journal Nature Geoscience to reproduce conditions within Earth and indicate how the mantle controls core dynamics.

The method

By comparing their numerical simulations to recent global magnetic field models they have successfully reproduced the morphology of the intensity, direction, and time variability of the Earth's magnetic field and the associated large-scale flow structure at the top of the core. These simulations reveal that the long-term geomagnetic signatures of thermal core–mantle interactions are evident in the longitudinal structure of the geomagnetic field as equatorial patches of reverse flux, rather than the high-latitude patches suggested by less Earth-like simulations.

Magnetic fields generated in the simulations were also compared against observational records of Earth’s magnetic field, considering measurements from the past 400 years as well as reconstructions from geological samples covering the past 100,000 years.

Comparison of these simulations with the field models suggests that the amplitude of the present-day longitudinal hemispheric imbalance in secular variation (i.e., the continuous drift in the intensity and direction of the Earth's magnetic field) is anomalously large, indicating our present-day geomagnetic field may be unusual.

Next steps

Researchers are now working with palaeomagnetists to test whether there is observational evidence of the influence of the mantle on Earth’s magnetic field over geological timescales. If so, it might be possible to determine how the pattern of mantle convection has changed through time. By collaborating with seismologists, it is possible to test whether the regions within the core where the mantle suppresses convection are seismically distinct from the bulk of the core.

Edited from Nature Geoscience Research Briefing "The mantle’s influence on the long-term behaviour of Earth’s magnetic field"