Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p31c1254a&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P31C-1254
Physics
[1510] Geomagnetism And Paleomagnetism / Dynamo: Theories And Simulations, [1521] Geomagnetism And Paleomagnetism / Paleointensity, [1560] Geomagnetism And Paleomagnetism / Time Variations: Secular And Longer
Scientific paper
Measurement of Earth’s magnetic field intensity from sedimentary rocks confirms that the field is a transient on millennial time scales. In accounting for this observation, parameters from dynamo models need to be compared with those obtained from observations. Here we model temporal changes in intensity of the geomagnetic field as either growths or decays, sometimes separated by stationary states. In order to obtain temporal properties of the geomagnetic field, our model, developed as a Matlab algorithm, searches records of relative paleointensity to measure objectively the rates of growth and decay of the field. Here we report on the application of our algorithm to six records of relative paleointensity obtained from oceanic cores. Our model for the fluid velocity field in Earth’s core is based on parametric instability produced externally through gradients of the gravitational field. It is well known that these gradients can lead to instability of the core fluid through both elliptical and shear straining of fluid streamlines. Such an instability will exist as long as the externally produced strain rate exceeds the dissipation rate in Earth’s fluid core. As known from both theoretical models and experimental observations that a sequence of alternately growing and decaying velocities will develop in the fluid, our algorithm has searched the records of relative paleointensity for exponential growths and decays. Since a balance may exist between strain and decay rates described above, our algorithm includes the possibility for a segment of relative paleointensity that is stationary. Such segments do indeed occur in the relative paleointensity record and are expected by the model of parametric instability. Results of the application of our algorithm spanning two Ma with broad geographical coverage will be presented.
Aldridge Keith D.
Baker Robin R.
McMillan D. G.
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