Earth magnetic field modeling from Oersted and Champ data

Abstract

We present a method to model geomagnetic field requiring only a restricted number of measurements on magnetic survey satellite orbits. These points are chosen in an optimal-or close to optimal-manner relying on recent developments in the problem of numerical integration over spheres. The method allows us to compute a series of models at short time intervals, namely 10 days in the present study. At each of these close dates several models are computed from independent sets of data; their redundancy in turn provides a control of results thanks to which the selection of data-for example, as a function of magnetic activity or latitude-may be reduced. We find that the internal low degree Gauss coefficients derived from Oersted and Champ data, respectively, differ from one another by 1 or 2 nT. We then take as a second example of the method application a brief study of the so-called external field. We compare the first-degree axisymmetric field with the D st index.

Rare palaeomagnetic evidence of long-term mantle control of the geodynamo and possible role of the NAD field in the reversal process

“…This flux feature is also clearly observed from measurements of more recent magnetic survey satellite orbits (e.g. Le Mouël et al 2010). We argue that this surprisingly strong correspondence between Cenozoic transitional fields and the pattern of radial flux presently leaving the outer core provides to date the most significant evidence of tight, long-term mantle control of transitional field morphologies.…”