Planetary Group Seminar: Magnetic constraint of core flow in Earth and Jupiter (R. Holme)

The strongest probe of changes with the interior of the earth is the change in the geomagnetic field with time, its so-called secular variation. This change is interpreted as being due to the transport of magnetic field by the flow generated by the planetary dynamo process, allowing changes in field to model this generating flow. In the Earth, such flows have been modelled for almost 40 years, but the basic assumptions have been changed by recent results from seismology and mineral physics, suggesting that the top of the core may be stably stratified. A stably-stratified layer supports a new set of modes, analogous to those seen in the atmosphere and oceans, which provide a very clean explanation for various features in the secular variation, particularly the approximately 60-year oscillation in the dipole field, and some rapid changes in the geomagnetic field, so-called “geomagnetic jerks”. These features are also linked to Earth rotation oscillations on much shorter time scales – I discuss whether these two views can be brought together.
Until recently, the Earth has been the only planet for which we have sufficiently detailed magnetic observations to allow flows to be calculated. However, the field of Jupiter has been observed for almost 50 years, and reanalysis of past field observations have suggested a model of secular variation can also be constrained at Jupiter. I present this model and the flow it implies, in full knowledge that the upcoming Juno mission, due to arrive at Jupiter in July, may prove me completely wrong! I discuss briefly what data from this mission may be provided, and what results we may anticipate concerning internal magnetic field and planetary motions at Jupiter.