Development of a New Model for Short Period Ocean Tidal Variations of Earth Rotation

Abstract:

Within project SPOT (Short Period Ocean Tidal variations in Earth rotation) we
develop a new high frequency Earth rotation model based on empirical ocean tide
models. The main purpose of the SPOT model is its application to space geodetic
observations such as GNSS and VLBI.
The advantage of empirical ocean tide models is their independency of any
hydrodynamical ocean model and its inherent assumptions and simplifications. We
use here the EOT11a model of Savcenko & Bosch (2012), which is extended for
some additional minor tides (e.g. M1, J1, T2). Furthermore, the number of tidal
constituents in the model is increased from 71 (IERS conventional model) to 120,
by which additional minor tides are considered for the admittance approach.
As empirical tidal models do not provide ocean tidal currents, which are required
for the computation of oceanic relative angular momentum, we implement
an approach first published by Ray (2001) to estimate ocean tidal current velocities
for all tides considered in the extended EOT11a model. The approach itself is
tested by application to tidal heights from hydrodynamic ocean tide models, which
also provide tidal current velocities. Based on the tidal heights and the associated
current velocities the oceanic tidal angular momentum (OTAM) is calculated.
For the computation of the related short period variation of Earth rotation, we
have re-examined the Euler-Liouville equation for an elastic Earth model with a
liquid core. The focus here is on the consistent calculation of the elastic Love numbers
and associated Earth model parameters, which are considered in the Euler-
Liouville equation for diurnal and sub-diurnal periods in the frequency domain.
We combine the observed tidal heights, estimated tidal current velocities and
calculated response of an elastic Earth to our improved model of short period ocean
tidal variation of Earth rotation. The preliminary version is used in the analysis of
VLBI data (e.g. CONT11), which enable us to evaluate independently the preliminary
model and to improve it further in a next step.