Detection of the Atmospheric S₁Tide in VLBI Polar Motion Time Series

The contribution of the diurnal atmospheric S₁ tide to Earth’s wobble is assessed by tidally analyzing hourly polar motion (PM) estimates from approximately 25 years of geodetic Very Long Baseline Interferometry (VLBI) observations. Special emphasis is placed on the dependency of S₁ estimates on various settings in the a priori delay model and on the method of time series analysis in post-processing. The considered VLBI solutions differ with regard to the inclusion/exclusion of weak network geometries and the choice of a priori geophysical corrections such as thermal antenna deformation. Prograde PM coefficients \(\text{A}^{+} + i\text{B}^{+}\) of S₁ are on the level of 9 + i10 μas (microarcseconds) for all solutions and none of the changes in the processing strategies perturbs this estimate beyond the twofold S₁ standard deviation (\(\sim\) 2.6 μas). An independent validation of the deduced harmonics against excitation estimates from atmosphere-ocean models shows that space geodetic and geophysical accounts of the S₁ effect in PM are still inconsistent by about 10 μas.