Earth's core contribution to variations in length of day

Abstract:

Exchanges of axial angular momentum between the Earth's core and the mantle lead to variations in the rotation rate of the mantle, observed as length of day (LOD) variations. LOD changes at decadal timescale are dominantly the result of core-mantle angular momentum exchanges. This is verified based on predictions of the changes in core angular momentum calculated on the basis of flows that can explain the observed changes in Earth's magnetic field. Similarly, a periodic LOD change with a period of approximately 6 years can also be shown to be of core origin. We expect that core flow variations at longer timescale (hundreds of years) should also lead to LOD changes though this is more difficult to confirm with available data on Earth rotation. While the core contribution to LOD changes at decadal timescale and for the 6 year signal is well established on the basis of angular momentum budget, the nature of the torque responsible for the angular momentum exchange remains a question mark. In this presentation, I will review our knowledge of the core contribution to LOD changes. I will also present results from recent attempts at identifying the nature of the torque between the core and mantle.