Abstrakt
Space geodetic determinations of a 6s length-of-day (LOD) anomaly at the diurnal S-1 frequency are reconciled with excitation estimates from geophysical fluid models. Preference is given to a hybrid excitation scheme that combines atmospheric torques with oceanic angular momentum (OAM) terms from hydrodynamic forward modeling.
A joint inversion of all data sets yields an LOD in-phase and quadrature estimate of (5.91, -0.22)s, matching space geodetic S-1 terms well within their formal uncertainties. Non-harmonic LOD excitations, while less than 30% of the time-averaged rotation rate contribution, are conclusively linked to El Nino-Southern Oscillation (ENSO) as the main perturbation of diurnal cycle characteristics in the troposphere.
ENSO modulations of particular relevance are those in OAM, associated with the barotropic ocean response to regional modifications in the diurnal atmospheric pressure wave. The study thus highlights previously unexplored aspects of non-tidal mass-field variability in the Earth system.