UMD Geology: Buffett on the origins of Earth’s magneit field

2015 Geology Colloquium Series
Friday, September 18th 2015 at 3:00 pm
in PLS 1140
Bruce Buffett
University of California, Berkeley
Geomagnetic reversals and excursions: Insights into the origins of Earth’s magnetic field
Palaeomagnetic observations offer important insights into the origin of Earth’s interior, but a detailed reconstruction of the underlying dynamics is not feasible. A practical alternative is to construct a stochastic model for the time evolution of the dipole field. Slow changes in the field are described by a deterministic (drift) term, whereas short-time fluctuations are represented by a random (noise) term. Estimates for the drift and noise terms can be recovered from a time series of variations in the axial dipole moment over the past 2 million years. The results are used to predict a number of statistical properties of the palaeomagnetic field, including the average rates of magnetic reversals and excursions. A physical interpretation of the stochastic models suggests that reversals and excursions are part of a continuum of time variations in Earth’s magnetic field, arising from convective fluctuations in the core. Relatively modest changes t! he amplitude of convective fluctuations can produce large changes in reversal rates, including the well-known occurrence of superchrons lasting longer than 10 million years.


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