抄録
Since the first time geomagneticists tried to derive the expression of the fluid flow at the top of the core, various assumptions have been made in order to reduce first, the non-uniqueness and second, the number of free parameters of the problem. We show that a geostrophic flow with a plane reflexion symmetry about the equatorial plane and a simple symmetry about the Earth's centre for the non-zonal component accounts for the 1980 secular variation (S.V.) although the number of parameters of the flow is reduced by a factor eight (from the number necessary when no assumption is made); the relative misfit between the predicted and the observed S.V. is of the same order as those existing between various 1980 S.V. models. The so-obtained flow exhibits a rather simple configuration. We suggest a means of downward continuing the flow into the body of the core which leads to some integral constraints on the density heterogeneity in the core.
