Fluid upwelling at the core–mantle boundary – resolvability from surface geomagnetic data

Abstract

The ability of geomagnetic secular variation data collected at the Earth's surface to resolve integrals of the radial field component over patches of the core‐mantle boundary is examined using linear inverse theory. It is shown that the usual modelling procedure is bound to give poor averaging functions for patches covering almost hemispheric regions of the core‐mantle boundary, regardless of the surface data distribution, and a resolving criterion producing more satisfactory functions is defined. For just 318 data, these averaging functions are a rather poor approximation to the ideal, and the error on the patch integral estimates incurred by imperfect resolution far exceeds that due to the mapping of the errors on the original data into the solution. A considerably larger dataset is needed to improve the resolution sufficiently to provide a stringent test of the ‘no upwelling’ hypothesis, which requires that all patch integrals of a certain type vanish. Copyright © 1984, Wiley Blackwell. All rights reserved