Numerical models of the geodynamo and
observational constraints
Emmanuel Dormy, Jean-Pierre Valet, and Vincent Courtillot
Institut de Physique du Globe de Paris,
Laboratoire de Géomagnétisme et Paléomagnétisme,
4, place Jussieu, 75252 Paris cedex 05, France.
Geochem. Geophys. Geosyst., vol. 1, Paper number 2000GC000062
(2000)
Abstract. The past few years have seen the emergence of a large number of numerical
simulations of the geodynamo. In parallel, both new and old geomagnetic,
archeomagnetic, and paleomagnetic observations have been interpreted as actual
geomagnetic features and used as constraints for dynamo models. Naturally,
model predictions should be tested against actual characteristics of the
geomagnetic field. Despite huge differences (sometimes in excess of a billion)
between the values of parameters used in the simulations and those estimated for
the Earth, it is intriguing that many available simulations succeed in producing
largely axial dipolar magnetic fields with weaker nondipolar structures, in
agreement with the first-order characteristics of the geomagnetic field. Yet, when
considering finer characteristics, there are significant differences, and failures to
actually produce a number of fundamental characteristic features. In this
presentation, we first review numerical results obtained to date, then we attempt
to summarize which field characteristics derived from observational data sets can
be considered robust. On the basis of simple criteria used to evaluate the degree
of confidence that can be placed in each datum, we sort presumably characteristic
geomagnetic features into three categories (robust, controversial, and unlikely).
We conclude that numerical models should be illustrated with a number of key
"predictions," averaged over at least 10 dipole diffusion times. These predictions
should be tested against the subset of robust observations only. Controversial
observations should await additional confirmation.
Key Words: Geodynamo; Earth core; geomagnetic field; magnetic records.