Geomagnetic dipole moment collapse by convective mixing in the core
- Creators
- Liu, Lijun
- Olson, Peter
Abstract
Convective mixing in the fluid outer core can induce rapid transient decrease of the geomagnetic dipole. Here we determine rates of dipole moment decrease as a function of magnetic Reynolds number following convective instability in a numerical dynamo and in axisymmetric kinematic flows. Our calculations show that mixing flows induce reversed magnetic flux on the core-mantle boundary through expulsion of mostly poloidal magnetic field by convective upwellings. The dipole field collapse is accelerated by enhanced radial diffusion and meridional advection of magnetic flux below the core-mantle boundary. Magnetic energy cascades from the dipole to smaller scales during mixing, producing a filamentary magnetic field structure on the core-mantle boundary. We find that the maximum rate of dipole moment decrease on century time scales is weakly sensitive to the mixing flow pattern but varies with the velocity of the flow approximately as cRm^β , with Rm the magnetic Reynolds number and (c, β) ≈ (0.2 ± 0.07, 0.78 ± 0.05). According to our calculations, a mixing flow in the outer core with Rm in the range of 200–300 can account for the historically-measured rate of decrease of the geomagnetic dipole moment, although it is unlikely that a single mixing flow event with this intensity would cause a full dipole collapse or polarity reversal.
Additional Information
© 2009 American Geophysical Union. Received 12 March 2009; accepted 24 April 2009; published 28 May 2009. This research was supported by grant number EAR-0604974 from the Geophysics Program of the National Science Foundation.Attached Files
Published - Liu2009p4489Geophys_Res_Lett.pdf
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Additional details
- Eprint ID
- 15060
- Resolver ID
- CaltechAUTHORS:20090817-092801594
- EAR-0604974
- NSF
- Created
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2009-08-18Created from EPrint's datestamp field
- Updated
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2021-11-08Created from EPrint's last_modified field