A series of computer simulations of the Earth's dynamo illustrates how the thermal structure of the lowermost mantle might affect convection and magnetic-field generation in the fluid core. Eight different patterns of heat flux from the core to the mantle are imposed over the core–mantle boundary. Spontaneous magnetic dipole reversals and excursions occur in seven of these cases, although sometimes the field only reverses in the outer part of the core, and then quickly reverses back. The results suggest correlations among the frequency of reversals, the duration over which the reversals occur, the magnetic-field intensity and the secular variation. The case with uniform heat flux at the core–mantle boundary appears most ‘Earth-like’. This result suggests that variations in heat flux at the core–mantle boundary of the Earth are smaller than previously thought, possibly because seismic velocity anomalies in the lowermost mantle might have more of a compositional rather than thermal origin, or because of enhanced heat flux in the mantle's zones of ultra-low seismic velocity.
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We thank R. T. Merrill for suggesting this numerical study. This work was supported by the Institute of Geophysics and Planetary Physics, the Los Alamos LDRD program, the University of California Research Partnership Initiatives program, the NSF Geophysics program and the NASA HPCC/ESS Grand Challenge program. Computing resources were provided by the Los Alamos Advanced Computing Laboratory, the San Diego Supercomputing Center, the Pittsburgh Supercomputing Center, the National Center for Supercomputing Applications, the Texas Advanced Computing Center, the Goddard Space Flight Center, and the Marshall Space Flight Center.
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Glatzmaier, G., Coe, R., Hongre, L. et al. The role of the Earth's mantle in controlling the frequency of geomagnetic reversals. Nature 401, 885–890 (1999). https://doi.org/10.1038/44776
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