Changes in Earth's core-generated magnetic field, as observed by Swarm

By far the largest part of the Earth's magnetic field is generated by motions taking place within our planet's liquid metal outer core. Variations of this core-generated field thus provide us with a unique means of probing the dynamics taking place in the deepest reaches of the Earth. In this contribution, we will present the core-generated magnetic field, and its recent time changes, as seen by ESA's Earth explorer mission Swarm.

We will present a new time-dependent geomagnetic field model, called CHAOS-6, derived from satellite data collected by the Swarm constellation, as well as data from the previous missions CHAMP and Oersted together with ground observatory data. Advantage is taken of the constellation aspect of the Swarm mission by ingesting field differences along track and across track between the lower pair of Swarm satellites.

Evaluating the global field model at the outer boundary of the source region, the core-mantle boundary, we present maps of the detailed structure of the geodynamo, and how this is presently evolving. Both the trend (secular variation) and accelerations in the field changes since the launch of the Swarm mission will be presented.

Assuming that field changes are primarily a result of advective processes, thanks to the high electrical conductivity of the core, and that the responsible core flows are essentially columnar, due to the organizing influence of the Coriolis force, we derive maps of the underlying core flow. The structure of this core flow, its changes over recent years, and implications for our understanding of the geodynamo process will be discussed.