The possible 5.9 years oscillation identification from superconducting gravimeter observations

Abstract

Abstract. Surface gravity changes aroused by the periodic ∼5.9 years oscillation (referred to as SYO) are important for understanding its origin and may further constrain Earth’s deep interior dynamics, but such signals have not been directly observed. In this study, we combine multiple spectra methods to analyze six usable superconducting gravimeter (SG) residual series in Western Europe, Canada, and Australia between 1996 and 2019; and try to extract the possible SYO signals from surface gravity observations. The amplitudes of the recovered possible SYO gravity changes vary from 0.5 to 0.9 μGal at different observatories. Comparisons with a derived time‐varying gravity model indicate that the phases of gravity SYO may also have a spherical harmonic Y22 spatial distribution. The corresponding amplitude transform factors δ/h between the observed and modeled signals for different SG stations are about 2.9, greater than the ratio of ~1.9 for the corresponding tidal Love numbers. The observed amplitudes are also quite different from the predictions of the possible mechanisms suggested by previous studies. Although the SYO is believed to have originated from core motions, our findings mean that the potential physical mechanism should be much more complicated than any existing one. We suggest that the MAC waves arising from the interplay between Magnetic, Archimedes, and Coriolis forces could be a possible excitation source of the SYO. We believe our gravity observation results should help interpret the SYO in the future.