Periods of extreme geomagnetic change such as geomagnetic excursions have frequently occurred throughout geological time. Characterizing their behaviour is essential for a full understanding of the geodynamo and the interaction of Earth's magnetic field and the space environment.
We model the global behaviour of Earth’s magnetic field between 10 and 50 ka using palaeomagnetic data. During this time the geomagnetic field showed significant variability in direction and intensity, including two well documented excursions: Laschamp and Mono Lake. No model currently exists that spans the total length of this time period, yet this period could provide great insights into the geodynamo. The ultimate goal of the project is to synthesize the results from our empirical modelling with those from numerical dynamo simulations, so that a deeper physical understanding of geodynamo processes can be gained.
We first compile all sedimentary and volcanic palaeomagnetic data coupled with geochronological data spanning this period in the GEOMAGIA.v3 database. This data is added to a community available database along with all rock magnetic and sedimentological metadata. This allows a detailed assessment of the data used in the modelling. Low quality palaeomagnetic data and erroneous age models may distort geomagnetic field structures generated by our new model and it is a key objective of this study to assess the fidelity of the palaeomagnetic and chronological data included in the modeling.
Using this data we then construct a temporally continuous global spherical harmonic geomagnetic field model through a regularized least squares inversion of the data using spherical harmonics in space and cubic B splines in time. This model enables assessment of the geomagnetic at the core-mantle boundary, the Earth’s surface and at elevated altitudes. Our key scientific objective is to determine where excursions fit into the spectrum of geomagnetic field variations and how the geodynamo processes that generate excursions differ from those that produce secular variation and reversals.