Mean electromotive force generated by asymmetric fluid flow near the surface of Earth's outer core

Abstract

The φ -component, ε_φ , of the mean electromotive force ε → generated by asymmetric flow of fluid just beneath the core-mantle boundary (CMB), is obtained using a geomagnetic field model. This analysis is based on the supposition that the axisymmetric part of fluid flow beneath the CMB is tangentially geostrophic and toroidal. For all the epochs studied, the computed ε_φ is stronger in the southern hemisphere than that in the northern hemisphere. Assuming a linear relationship between ε → and the azimuthally averaged magnetic field B → 0 , the only non-zero off-diagonal components of the pseudotensor α_ij relating ε → to B → 0 , are estimated as functions of colatitude θ and the physical implications of the results are discussed.