The geomagnetic field is generated by fluid flow in the metallic liquid outer core, a process known as the geodynamo. Due to its current strength and mainly dipolar geometry, this field efficiently organizes the way particles flow in the vicinity of the Earth, preventing them from directly reaching the atmosphere. Currently however, the geomagnetic dipole decays 10 times faster than the free decay rate. Understanding the mechanisms responsible for this rapid evolution is then both a practical issue - predicting the future morphology of the magnetosphere and areas of danger in space - and a fundamental one - understanding the inner working of the geodynamo.
This proposal aims at studying the possible influence of core-mantle interactions in defining the main characteristics of the current geomagnetic field, and the mechanisms governing its evolution. To achieve this, we will combine geomagnetic data analysis, dynamo simulations, and seismic imaging. Such an approach is now accessible for extensive studies, thanks to the availability of more and more high quality geomagnetic and seismological observations, and of much more affordable numerical dynamo codes. Geomagnetic secular variation (SV) data will be inverted for flow models below the core-mantle boundary. Lower mantle tomography data will be used to infer density anomalies and mantle-driven thermal wind flows at the top of the core. Numerical dynamo simulations will be used to model core flow driven by convection at the outer core.
Comparisons between all those flow models will be used to infer mantle control on core flow. Geomagnetic data and core flow models will otherwise be used to compute contributions of meridional advection, radial diffusion and meridional diffusion to the decrease of the geomagnetic dipole moment. A similar analysis will be done on numerical dynamo simulations. The two approaches will be combined to identify and quantify dynamo mechanisms of dipole moment decrease.
Fields of science
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