Potential links between internal and external geodynamics at periods around 6 years

The GRACEFUL project aims to better understand dynamic processes in the Earth’s deep interior using a combination of satellite observations of the Earth’s magnetic field, gravity field, and rotation. Significant oscillations at periods ranging from 6 to 8 years have been linked to dynamical processes in the fluid outer core and at the core-mantle boundary, influencing the three aforementioned observables. However, the occurrence of a 6-year cycle was also recently evidenced in the climate system, expressed in the global mean surface temperature, zonal winds, precipitation, terrestrial water storage changes, sea level changes, and ice mass changes. This study provides a comprehensive review of the 6-year cycle observed across the entire Earth system, from its deep interior to its fluid external envelopes. We propose several mechanisms that could explain small amplitude variations in geodetic observations, such as the length of day and gravity field, highlighting potential links between internal and external geodynamics at periods of around 6 years.