Geophysical Fluid Contributions to Intradecadal Length of Day Variations

Variations in length of day (LOD) are a result of mass movements in the Earth's fluid envelope and deep interior. Previously, a six (SYO) and eight year (EYO) oscillation have been inferred to arise from fluid motions in the core; however, these signals are masked by other geophysical fluid contributions. This work focuses on assessing the impact of atmospheres, oceans, and hydrology on studying the SYO and EYO. To isolate these oscillations for further study, we subtracted angular momentum contributions originating from zonal tides, the atmosphere, oceans, and hydrology. Zonal tides are subtracted based on a synthetic model utilising a sum of harmonic waves. Atmospheric contributions are subtracted to isolate the SYO and EYO, as a result of atmospheric interference within the four to seven year range. Oceanic contributions made little difference to the analysis of the LOD signal; thus, removal of these contributions is not required within the intradecadal time scale. Hydrologic contributions were not removed for our analysis of the SYO and EYO, as including hydrologic contributions resulted in a cleaner isolation of the SYO and EYO. We conclude that studies analysing intradecadal LOD variations should remove tidal and atmospheric contributions, oceanic contributions have minimal impact, and hydrological contributions mask our signal.