Investigation of the time variability of diurnal tides and resonant FCN period

• Comparison of different methods and data of worldwide SG stations and VLBI.
• Variation of FCN period totally depends on Ψ1 tidal wave and −365.26 nutation.
• Similar decadal variation exists in FCN period obtained from SG and VLBI data.
• Variation in FCN period has possible correlation with the decadal LOD trend.

The time variability of diurnal tides was investigated by analyzing gravity observations from global superconducting gravimeter (SG) stations with running time intervals. Through least-square and Bayesian approaches, FCN resonance parameters were estimated for each data section after obtaining the tidal parameters of mainly diurnal tidal waves. The correlation of the time variation in diurnal tidal waves and FCN period was discussed. For comparison, a similar method was used to analyze VLBI observations to study the time variability of nutation terms and FCN period. The variation trend of the FCN period totally depends on the Ψ1 wave in tidal gravity and on the retrograde annual term in nutation. We observed a similar variation trend in the FCN periods obtained from different SG stations worldwide and VLBI observations. The relation between diurnal tides and LOD variations is discussed and the possible mechanisms of the decadal variation in FCN periods were discussed.