The 2013 Petrus Peregrinus Medal is awarded to Dominique Jault for outstanding research in geomagnetism and the dynamics of the Earth’s core. His seminal work linking changes in the length of day to core flows consistent with the geomagnetic secular variation helped establish a new understanding of core processes. His subsequent research has added greatly to our understanding of the Earth’s deep interior.
Dominique Jault was lead author of a Nature paper in 1988 that made a remarkable breakthrough in our understanding of the Earth’s core. Starting with observations of the geomagnetic secular variation, he and his collaborators worked out the axisymmetric part of the core flow using tangentially geostrophy, which reflects the dominance of rotation in core dynamics. They went on to compute the decadal angular momentum changes in the Earth’s core resulting from these flows, and to show that these angular momentum changes were in excellent agreement with the observed decadal changes in the length of day. This transformed the study of core dynamics from an interesting theoretical exercise into a subject whose results could be directly tested against observation, thus putting the whole subject on a much sounder scientific basis.
Jault went on to add greatly to the physical and mathematical basis of dynamo theory. A hallmark of his work has been to establish the connection between the complex mathematics of dynamos and the observations of the geomagnetic field. More recently, Jault returned to the problem of torsional oscillations and another key Nature paper has recently emerged from his group. This work promises an observational constraint on the strength of the magnetic field in the deep interior of the core, an issue which has provoked much debate in the past.
Jault has also made an important impact on laboratory experiments investigating rotating magnetohydrodynamics (MHD), relevant to the conditions inside the Earth’s core. He played a significant role in setting up the Derviche Tourneur Sodium (DTS) experiment in Grenoble, and he has been at the forefront of the task of translating the experimental observations into understanding the interaction of rotation and magnetic fields. A spectacular success has been the experimental verification of the super-rotation phenomenon: magnetic fields can lead to fluid in the outer core rotating faster than the inner core, even when the outer sphere is held stationary. This counter-intuitive result was predicted by mathematical analysis of the rotating MHD equations, but the DTS observations have given the community much more confidence in the underlying theory.
In addition to his research achievements, Jault has played a key role in establishing and directing the highly successful Laboratoire de Géophysique Interne et Tectonophysique in Grenoble, now part of the Institut des Sciences de la Terre. This group, together with the young scientists originally trained in Grenoble, are key players in the rapidly developing area of deep Earth research, and much of this remarkable success can be attributed to Jault’s profound understanding of geomagnetism.