Effective Angular Momentum Budget Misclosure Across Time Scales: Highlighting the Role of Oceanic Uncertainties

The conservation of Earth’s total angular momentum provides a fundamental constraint linking geodetic observations of Earth rotation to geophysical excitation processes. The closure of effective angular momentum (EAM) budgets remains incomplete, particularly across temporal scales, due to remaining model and data uncertainties that complicate the consistent capture of mass- and motion-related contributions from geophysical forcing. In this study, we investigate the closure of EAM budgets by systematically combining atmospheric (AAM), oceanic (OAM), and hydrological (HAM) angular momentum estimates and comparing them to geodetic angular momentum (GAM) derived from the latest EOP 20 C04 time series of the IERS.

Our analyses focus on the GRACE/-FO era (2002–2022) using daily temporal sampling, with extensions to earlier epochs (back to 1970) for selected datasets. GAM estimates are computed from polar motion and length-of-day observations using Chandler wobble deconvolution and tidal corrections. Available to us are EAM from various atmospheric reanalyses, land surface models and monthly-mean GRACE/-FO gravity fields. A particular focus is placed on a small ensemble of OAM estimates from (i) MPIOM under different atmospheric forcings, (ii) DEBOT (a simple single-layer model) forced with MERRA-2, and (iii) several ECCO (a data-constrained ocean state estimate) realizations. All EAM data are processed through detrending, offset removal, and explicit separation of seasonal, interannual, and higher-frequency variability using harmonic fitting and Butterworth filtering.

Frequency spectra analyses reveal substantial discrepancies among the OAM estimates, particularly at sub-monthly and interannual time scales, suggesting that uncertainties in oceanic angular momentum and its underlying models represent a major limitation for the EAM budget closure. Our ongoing work aims to quantify the impact of different excitation combinations, temporal scales, and mass versus motion terms on residual budget misclosure.