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Abstract:
Earth’s magnetic field is generated by a dynamo acting within its liquid-iron outer core. This process is ultimately controlled by the rate at which the mantle extracts heat from the core. Because convection in the silicate mantle occurs on much longer time and length scales than convection in the core, the existence of mantle features such as the Large Low Velocity Provinces results in strong lateral variations in heat flow across the core-mantle boundary. We have undertaken numerical simulations of this situation to determine how the mantle controls core dynamics and hence the structure and temporal variability of the magnetic field. We compare these simulations to recent magnetic field models, based on observational data spanning tens of thousands of years, and find that they successfully reproduce the morphology and secular variation of Earth’s modern field as well as the inferred large-scale flow structure at the top of the core. Our simulations reveal that the long-term geomagnetic signatures of thermal core-mantle interactions are evident as equatorial patches of reverse flux, in addition to the high-latitude patches suggested in previous work. Comparison of our simulations with the observational models also suggests that the amplitude of the present-day longitudinal hemispheric imbalance in secular variation (i.e., “the quiet Pacific”) is anomalously large, indicating our present-day geomagnetic field may be unusual in this respect.
