Response of Earth's magnetic field to large lower mantle heterogeneity

Sahoo, S and Sreenivasan, B (2020) Response of Earth's magnetic field to large lower mantle heterogeneity. In: Earth and Planetary Science Letters, 549 .

	PDF ear_pla_sci_let_549_2020.pdf - Published Version Restricted to Registered users only Download (3MB) | Request a copy
	PDF 1-s2.0-S0012821X20304519-mmc1.pdf - Published Supplemental Material Restricted to Registered users only Download (4MB) | Request a copy

Abstract

A simplified two-fold pattern of convection in the Earth's core is often used to explain the non-axisymmetric magnetic flux concentrations in the present day geomagnetic field. For large lateral variations in the lower mantle heat flux, however, a substantial east�west dichotomy in core convection may be expected. This study examines the effect of a large lateral variation in heat flux at the outer boundary in cylindrical annulus experiments that achieve approximate geostrophy of the convection as well as in rapidly rotating spherical shell simulations. In either geometry, the imposed boundary heat flux is derived from the seismic shear wave velocity in the lowermost mantle. The pattern of large-scale convection in the simulations closely follows that in the annulus experiments, which suggests that the lateral buoyancy at the equator essentially determines the structure of core convection. In particular, the location of a coherent downwelling that forms beneath Canada in mildly driven convection entirely switches over to the Siberian region in strongly driven states. Spherical dynamo models in turn show that this eastward migration of convection causes the relative instability or even the disappearance of the high-latitude magnetic flux in the Western hemisphere. Finally, large radial buoyancy causes homogenization of convection, which may place an upper bound for the Rayleigh number in the core.

Item Type:	Journal Article
Publication:	Earth and Planetary Science Letters
Publisher:	Elsevier B.V.
Additional Information:	The copyright of this article belongs to Elsevier B.V.
Keywords:	Buoyancy; Geomagnetism; Heat convection; Magnetic flux; Shear flow; Shear waves; Wave propagation, Boundary heat flux; Cylindrical annulus; Earth's magnetic field; Geomagnetic fields; Lateral variations; Magnetic flux concentration; Relative instability; Shear wave velocity, Heat flux, core (planetary); experiment; geomagnetic field; geostrophic flow; heat flux; heterogeneity; lower mantle; mantle convection; spatial variation, Canada
Department/Centre:	Division of Mechanical Sciences > Centre for Earth Sciences
Date Deposited:	31 Aug 2020 08:03
Last Modified:	31 Aug 2020 08:03
URI:	http://eprints.iisc.ac.in/id/eprint/66409

Actions (login required)

View Item