Motions at the top of the core which generate the observed Secular Variation (S.V.) field are computed. To reduce the well known ambiguity of the solution, two constraints are added: the flow is a large scale one and is geostrophic. The computed flow then has a very simple geometry; its poloïdal part is roughly axisymmetrical with respect to an equatorial diameter. This geometry is almost unchanged from 1970 to 1980 while the intensity of the velocity is nearly doubled. © 1985.
Le Mouël, J. L., Gire, C., & Madden, T. (1985). Motions at core surface in the geostrophic approximation. Physics of the Earth and Planetary Interiors, 39(4), 270–287. https://doi.org/10.1016/0031-9201(85)90140-2