Does Core-Mantle Boundary Heat Flow Regulate Geodynamo Reversal Frequency?

Details Does Core-Mantle Boundary Heat Flow Regulate Geodynamo Reversal Frequency? Does Core-Mantle Boundary Heat Flow Regulate Geodynamo Reversal Frequency?

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p31b1245o&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P31B-1245

Physics

[1510] Geomagnetism And Paleomagnetism / Dynamo: Theories And Simulations, [1535] Geomagnetism And Paleomagnetism / Reversals: Process, Timescale, Magnetostratigraphy, [8115] Tectonophysics / Core Processes, [8130] Tectonophysics / Heat Generation And Transport

Scientific paper

We analyze more than two hundred magnetic polarity reversals and excursions over forty million years of time from numerical dynamos with heterogeneous boundary heat flux. Comparisons between a dynamo with uniform boundary heat flux, dynamos with boundary heat flux patterns consisting of a single spherical harmonic, and dynamos with tomographic heat flux patterns proportional to the large-scale lateral variation of seismic shear wave velocity in the lower mantle reveal that boundary heat flux heterogeneity tends to increase the average frequency of polarity reversals relative to uniform boundary conditions, particularly if the heterogeneity increases the average equatorial heat flux. Non-axisymmetric spherical harmonic degree 1 and 2 boundary heterogeneity and the seismically-derived tomographic heterogeneity generally produce comparable reversal and excursion frequencies, indicating that geomagnetic polarity reversal rates may be insensitive to the non-axisymmetric planform of core-mantle boundary heat flux. In contrast, the average polarity reversal frequency in these models is sensitive to the total boundary heat flow and is also sensitive to the total heat flow at the equator, with non-reversing behavior at low heat flow and frequent reversals at high heat flow conditions, respectively. Our results suggest that geomagnetic superchrons may correspond to times with below average core-mantle boundary heat flux, either globally or equatorially, and conversely, periods with higher paleomagnetic reversal frequency may correspond to times with above average equatorial heat flux at the core-mantle boundary.

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