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SCORE

Simulating Oceanic Contributions to Earth Rotation

 

Funding Agency

FWF - Der Wissenschaftsfonds

Duration (TU Wien)

01.04.2017 – 31.01.2018

Duration (Bonn University)

01.02.2018 – 31.03.2020

Principal Investigator

Prof. Dr. techn. Michael Schindelegger

Contributing Scientists

M.Sc. Alexander Harker

M.Sc. Makan Karegar

Project Description

SCORE operates between the lines of geodesy and oceanography and addresses hitherto unconsidered aspects of Earth rotation dynamics that are linked to the ocean’s circulation and its mass-field variability on strictly diurnal and on sub-monthly time scales. The immediate motivation behind the study is for accurate oceanic angular momentum estimates to be used in a priori models of Earth rotation for space geodetic analysis, but implications also exist for satellite-gravimetry based climate sensors such as GRACE. Computational tools are an efficient high-resolution barotropic forward model and an elaborate 3D general circulation model, both of them applied to two distinct areas of operation.


First, we hypothesize that changes in the tropical weather due to the El Nino-Southern Oscillation (ENSO) enhance or weaken the daily cycle in the atmosphere and that the resultant pressure forces at the sea surface (see animation below) alter the oceanic tide of diurnal periodicity. The associated redistribution of water masses may be sufficiently strong to alter nutation (i.e., the swerving motion of the Earth in space) with magnitudes that can be detected in Very Long Baseline Interferometry data. Exploration of this signal specifically requires validation of atmospheric forcing data and multi-year ocean model simulations under changing ENSO conditions.

 

sup-mvA01.gif

Figure: ENSO-induced variations in the main atmospheric pressure tide S1 from a complex-valued EOF analysis over 2006–2012.
 

The study is then taken a step further to elucidate the relevance of some key components in the hydrodynamic equations for describing ocean-induced polar motion with periods from 2 to 20 days. Numerical experiments will be performed to assess the dependence of Earth rotation results on horizontal model resolution, the formulation of energy dissipation, and the rigorous consideration of self-attraction and loading feedbacks on moving water masses. The outcome of these simulations should be an optimally-configured barotropic ocean model capable of reducing remaining discrepancies between observed and geophysically modeled polar motion signals.
 

References

  • Schindelegger, M., Salstein D., Einšpigel D., Mayerhofer C. (2017), Diurnal atmosphere-ocean signals in Earth’s rotation rate and a possible modulation through ENSO. Geophysical Research Letters , 44(6), 2755–2762, doi:10.1002/2017GL072633.

  • Schindelegger, M., Quinn K., Ponte R. (2017), Oceanic signals in rapid polar motion: results from a barotropic forward model with explicit consideration of self-attraction and loading effects. Geohpys. Res. Abstracts, 19, EGU2017-12129, EGU General Assembly 2017.

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