Relationship between free core nutation and geomagnetic jerks

Abstract

Recent studies have indicated a correlation between Earth’s free core nutation (FCN) and geomagnetic jerks (GMJs). However, some uncertainties still need to be resolved before their relationship can be confirmed. The variations in the amplitude and phase of the FCN result from the comprehensive influence of the surface fluid layer and core–mantle couplings, which makes its correlation with GMJs difficult to verify. The FCN period mainly depends on the inertia coupling and the dissipative couplings (such as viscous, electromagnetic and topographic couplings) at the core–mantle boundary according to the theory of Earth rotation. Whatever the GMJ mechanism, it is most likely to affect the FCN by changing the core–mantle couplings. This study was conducted to effectively determine variations in the FCN period by considering atmospheric and oceanic effects, investigate any correlation between the two phenomena, and analyze how the FCN relates to GMJs. Using the normal time–frequency transform, we extracted signals in the nutation band from the atmospheric and oceanic angular momentum functions. We used the broadband Liouville equations to estimate the atmospheric and oceanic effects on nutation terms. Using a sliding window of 2 years, we fitted five nutation terms most affected by FCN resonance from the celestial pole offsets with FCN model removed. The FCN period variation was estimated by using weighted least square method. The results indicated a correlation between the FCN and GMJ. Further, we analyzed the relationship between the geomagnetic fluctuations and FCN based on both the core–mantle couplings and the possible GMJ mechanism.