Summary of the context and overall objectives of the project GRACEFUL

What is the problem/issue being addressed?

GRACEFUL is a project that will address fundamental shortcomings in the current understanding of the deep interior of our planet – in the fluid core in particular, with a long-term vision to open new frontiers and foster research on Earth’s interior by combining most up-to-date observations of the Earth gravity field, the magnetic field and the Earth rotation, as well as by developing precise modeling of the core flows.

The key scientific questions we want to address with this novel approach are:

  • What are the flow motions in the liquid core that can explain the observed magnetic field, its secular variation and its jerks, and that can explain the observed LOD variations at decadal and sub-decadal timescale?
  • What kind of global motion in the core is acting at these timescales?
  • What is the impact of core flow near the CMB on temporal gravity and LOD variations?
  • What is the role of the core, the core-mantle boundary and the lower mantle in explaining observed gravity, magnetic field and LOD variations?
  • Can we predict the changes in the flow of the core as well as in the magnetic field, LOD variations and core contributions on gravity?

Why is it important for society?

One needs to understand why the magnetic field is changing these days (even more rapidly than expected) and one needs to know the rotation of the Earth and orient the Earth very precisely in space, and therefore understand what is going on inside the core and at the core-mantle boundary.

The study of the Earth's deep interior is a discipline still in a period of important evolution and of great interest for the public. The accumulation of seismic data provides important information on the material and physical properties of the Earth's interior; however, only indirect observations are available on the dynamics of the Earth’s fluid iron-rich outer core. Apart from seismic waves, the magnetic and gravity fields, as well as the rotation of the Earth (in particular the Length Of Day, so-called LOD) provide invaluable information on processes occurring in the Earth's deep interior. The magnetic field, originating mainly within the Earth’s fluid outer core, and its temporal variations can be used to infer motions of the fluid core on decadal and sub-decadal time-scales. Temporal variations in the Earth's gravity field, which reflect changes in the mass distribution within the Earth and at its surface, occur on a broad range of time-scales, in particular in the decadal and interannual band. Such gravity changes are largely dominated by surface contributions related to the global water cycle and climate-driven land ice loss but they also include the gravitational signature of flow inside the core deforming the core-mantle boundary and penetrating/infiltrating the lower mantle. Changes in the Earth’s rotation, i.e. LOD variations, also occur on similar timescales, and are generally assumed to be caused by the motions in the fluid core through exchange of angular momentum at the core-mantle boundary. Scientific progress is most effective when combining observations and models. When a new source of observational data becomes available as well as novel techniques to analyse them, it can lead to a step change in our understanding of the observed system. In this project, we focus our effort to fully realize the potential of combining recent observations of the Earth gravity field, the magnetic field and the Earth rotation. We intend to use these observations in synergy, together with core flow models, to provide new information on the dynamical processes occurring in the fluid core and at the core-mantle boundary.