title: The Global S[Formula: see text] Tide in Earth's Nutation.
abstract: Diurnal S[Formula: see text] tidal oscillations in the coupled atmosphere-ocean system induce small perturbations of Earth's prograde annual nutation, but matching geophysical model estimates of this Sun-synchronous rotation signal with the observed effect in geodetic Very Long Baseline Interferometry (VLBI) data has thus far been elusive. The present study assesses the problem from a geophysical model perspective, using four modern-day atmospheric assimilation systems and a consistently forced barotropic ocean model that dissipates its energy excess in the global abyssal ocean through a parameterized tidal conversion scheme. The use of contemporary meteorological data does, however, not guarantee accurate nutation estimates per se; two of the probed datasets produce atmosphere-ocean-driven S[Formula: see text] terms that deviate by more than 30 [Formula: see text]as (microarcseconds) from the VLBI-observed harmonic of [Formula: see text] [Formula: see text]as. Partial deficiencies of these models in the diurnal band are also borne out by a validation of the air pressure tide against barometric in situ estimates as well as comparisons of simulated sea surface elevations with a global network of S[Formula: see text] tide gauge determinations. Credence is lent to the global S[Formula: see text] tide derived from the Modern-Era Retrospective Analysis for Research and Applications (MERRA) and the operational model of the European Centre for Medium-Range Weather Forecasts (ECMWF). When averaged over a temporal range of 2004 to 2013, their nutation contributions are estimated to be [Formula: see text] [Formula: see text]as (MERRA) and [Formula: see text] [Formula: see text]as (ECMWF operational), thus being virtually equivalent with the VLBI estimate. This remarkably close agreement will likely aid forthcoming nutation theories in their unambiguous a priori account of Earth's prograde annual celestial motion.
authors.affiliation: Department of Geodesy and Geoinformation, TU Wien, Gußhausstraße 27-29, 1040 Vienna, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Schindelegger
authors.affiliation: School of Cosmic Physics, Dublin Institute for Advanced Studies, Dublin, Ireland.|Department of Geophysics, Charles University in Prague, Prague, Czech Republic.
authors.forename: David
authors.initials: D
authors.lastname: Einšpigel
authors.affiliation: Atmospheric and Environmental Research, Inc., Lexington, MA USA.
authors.forename: David
authors.initials: D
authors.lastname: Salstein
authors.affiliation: Department of Geodesy and Geoinformation, TU Wien, Gußhausstraße 27-29, 1040 Vienna, Austria.
authors.forename: Johannes
authors.initials: J
authors.lastname: Böhm
keywords: Atmospheric tides; Earth rotation variations; Geophysical excitation; Nutation; Ocean tides