EGU General Assembly 2020
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A multi-model assessment of sub-monthly polar motion and the associated ocean bottom pressure variability

Michael Schindelegger1, Alexander Harker1, David Salstein2, and Henryk Dobslaw3
Michael Schindelegger et al.
  • 1Institute of Geodesy and Geoinformation, University of Bonn, Bonn, Germany (
  • 2Atmospheric and Environmental Research, Inc., Lexington, MA, U.S.A.
  • 3Deutsches GeoForschungsZentrum Potsdam, Potsdam, Germany

Budgeting geophysical fluid excitations against space-geodetic observations of polar motion reveals non-negligible residuals on sub-monthly time scales, typically 1−2 cm when projected onto the Earth's surface. A possible source for these discrepancies are imperfections in the hydrodynamic models used to derive the required ocean excitation functions. To guide future model improvements, we present a systematic assessment of the oceanic component of sub-monthly polar motion based on three global time-stepping models which are forced by the same atmospheric data but considerably differ in their numerical setup and physical parameterizations. In particular, we use ocean bottom pressure output and angular momenta from (i) the finite-element 2 Dimensions Gravity Wave Model (Mog2D), (ii) the baroclinic Max-Planck-Institute Ocean Model (MPIOM) at 1° horizontal resolution, representing the current industry standard, and (iii) a more experimental, eddy-permitting setup of the MITgcm (MIT General Circulation Model). Validations of data from 2007 to 2008 are performed against observed polar motion and daily GRACE (Gravity Recovery and Climate Experiment) solutions, which resolve the broad scales of ocean bottom pressure variability relevant for angular momentum considerations. No definite quantitative results are available at the time of this writing, but a specific question we aim to answer is whether the MITgcm run outperforms the other models in our validations, given its higher resolution and partial representation of flow interactions with major topographic features.

How to cite: Schindelegger, M., Harker, A., Salstein, D., and Dobslaw, H.: A multi-model assessment of sub-monthly polar motion and the associated ocean bottom pressure variability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7621,, 2020

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Display material version 2 – uploaded on 06 May 2020
Minor changes to text and figure captions.
  • CC1: Comment on EGU2020-7621, Christian Bizouard, 07 May 2020

    DEBOT ocean model: very impressive improvement below 10 days! 

    What is the period of study?

    Fig. 1: is it not the geodetic excitation residual (for x) rather than the pole coordinate x, which the computation requires an integration?

    • AC1: Reply to CC1, Michael Schindelegger, 07 May 2020

      Christian, thanks for your comment! For this particular poster, the simulations and analyses were done for a 2-year period (2007-2008), but we want to extend the records a bit. However, it will remain a "proof-of-concept" study rather than an introduction of a new operational product. Regarding Figure 1, that is indeed the polar motion residual in cm at the Earth's surface. I derived the series by multiplying the residual geodetic excitation function with the proper transfer function in the frequency domain and transforming the resulting Fourier coefficients back to the time domain.

      • CC2: Reply to AC1, Christian Bizouard, 07 May 2020

        Thnak you for your answer Michael! 

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