Ocean Model for Circulation and Tides (OMCT)

1. Ocean Model for Circulation and Tides (OMCT) based on the nonlinear momentum balance equation, the continuity equation, and conservation equations for heat and salt (Thomas 2002). The hydrostatic and Boussinesq approximations are applied. Water elevations, three‐dimensional horizontal velocities, potential temperature as well as salinity are calculated prognostically; vertical velocities are determined diagnostically from the incompressibility condition. A mass conserving approach for studying the impacts of global water storage changes on gravimetric time series Land Surface Discharge Model (LSDM) Global simulation of vertical and lateral water transport and storage changes on land surfaces (Dill 2008) Captures all major continental water mass transport processes (soil moisture, snow, rivers and lakes, runoff, drainage) Hartmut Wziontek1, Henryk Dobslaw2, Beatriz Cordoba3, Herbert Wilmes4 1, 4) BundesamtfürKartographie und Geodäsie, Leipzig and Frankfurt/Main, Germany. 2) Section 1.3: Earth System Modeling, DeutschesGeoForschungsZentrum, Potsdam, Germany. 3) Centro Astronomico de Yebes, InstitutoGeográficoNacional, Yebes, Spain. Besides mass changes in the vicinity of a gravimetric sensor, global redistribution of water is likely to affect High precision terrestrial gravity time series as obtained with Super-conducting gravimeters. To assess the quantity of the changing mass attraction, not only water storage changes of the continental hydrosphere have to be considered, but also the mass exchange and redistribution of masses in the oceans and in the atmosphere. In order to re-assess this effect, we use ECMWF's latest re-analysis ERA Interim together with simulated ocean bottom pressure from OMCT and terrestrially stored water masses from LSDM, which have been both consistently forced by ERA Interim. The mass attraction effect is computed globally from those data sets, and subsequently compared with measured gravity time series at selected stations of the Global Geodynamics Project (GGP). Superconducting gravimeters are the most sensitive and stable gravimeters available today. By comparison with absolute gravimeters, the scale factor and the (linear) drift are determined By this, continuous, high precision gravity time series are obtained. Here the so called ‘residuals’ after removing known signal at 4 stations are used Residual gravity times series from Superconducting Gravimeters at stations of the Global Geodynamics Project (GGP) Both models were consistently forced with ECMWF's latest re-analysis ERA Interim with mass, momentum, and energy fluxes from the atmosphere. Grids with a spatial resolution of 0.5 degrees and daily time steps for the period 2003-2009 were used Mass conserving models for terrestrial water storage changes and ocean mass redistribution: LSDM and OMCT 1) Federal Agency for Cartography and Geodesy (BKG)- Branch Office Leipzig -Karl-Rothe-Straße 10-14, 04105 Leipzig, GermanyTel : +49 (0) 341 56 34 – 256E-Mail: hartmut.wziontek@bkg.bund.de Summary Ocean mass variations from OMCT influences the attraction component of the far field at most and amounts up to several 10th of nm/s2. However, short –period variations appear, which are not visible in the signal measured by the SG. 4) Federal Agency for Cartography and Geodesy (BKG)Richard-Strauss-Allee 1160598 Frankfurt am Main, Germany Conclusions: Contact: 2) Helmholtz Centre PotsdamGFZ German Research Centre for GeosciencesTelegrafenberg14473 Potsdam, Germany Comparison of Gravity effects: Newtonian mass attraction and loading 3)Yebes Observatory Cerro de la Palera s/nYebes, 19141,Guadalajara, Spain Terrestrial water storage from LSDM and ocean mass variation from OMCT Terrestrial water storage from LSDM only Total gravity effect, including near field Far field effect SG030 and FG5-101 at the Geodetic Observatory Wettzell Loading effect Reduced gravimeter signal by total effect Mass distribution of terrestrial water storage from LSDMand non-tidal ocean variation from OMCT for 2009/04/15 Variance reduction of the SG measured gravity signal Residual gravity variations at three European and one South American GGP stations after removingthe effects of the Earth’s tides, atmosphere and polar motion. Total mass as obtained from ocean mass redistribution (OMCT), atmosphere (ERAi) and terrestrial water storage (LSDM). Total mass, split up into continental and oceanic part: Atmospheric pressure over land (ERAi), terrestrial water storage (LSDM) and ocean bottom pressure(OMCT). • The influence of ocean bottom pressure on the loading effect is rather small • Near field effects computed from LSDM fit fairly well to the SG observations - despite of the low spatial resolution of 0.5 degree • The application of global terrestrial water storage models was proofed again as a promisingtool to explain the residual SG signal. The completion with ocean mass variations improves the interpretation of seasonal features but needs further investigation for short periods. References: Dill, R., Hydrological model LSDM for operational Earth rotation and gravity field variations. GFZ Scientific Technical Report STR08/09, 2008. Dobslaw, H., R. Dill, A. Grötzsch, A. Brzeziński, and M. Thomas (2010), Seasonal polar motion excitation from numerical models of atmosphere, ocean, and continental hydrosphere, J. Geophys. Res., 115, B10406 Thomas, M. (2002), Ocean induced variations of Earth's rotation – Results from a simultaneous model of global circulation and tides, PhD dissertation, University of Hamburg, Germany Abstract number G21A-0743