Massentransporte und Massenverteilungen im System Erde  
    Altimetry helps to improve global ocean tides: the EOT08a modelAltimetry helps to improve global ocean tides: the EOT08a model  
 

 

Altimetry helps to improve global ocean tides: the EOT08a model

Analyzing nearly 15 years of altimeter data from different satellite missions a new global ocean tide model has been generated, providing amplitudes and phases for major diurnal and semi-diurnal constituents (K1, O1, Q1, M2, N2, S2, K2, 2N2) and the non-linear M4 tide on a dense 7.5'x7.5' geographical grid.

EOT08a - a new global ocean tide model

 

Caused by the attraction of Moon and Sun the ocean tides are the strongest, short-period water mass redistribution in the Earth system. Ocean tides have to be known with high precision if e.g. gravity field variations observed by GRACE are used to derive water mass redistribution of the continental hydrology known to be the most uncertain subsystem of the global water cycle.

 

An empirical analysis of nearly 15 years of harmonized and cross-calibrated multi-mission altimetry data now succeeded to generate a new global ocean tide model, EOT08a (Savcenko & Bosch, 2008). The model provides amplitudes and phases for major diurnal and semi-diurnal constituents (K1, O1, Q1, M2, N2, S2, K2, 2N2) and the non-linear M4 tide on a dense 7.5'x7.5' geographical grid. Compared to the FES2004 reference model EOT08a identifies residual amplitudes of up to 15 cm in shallow water like the Yellow Sea (Fig. 1). In open ocean there are extended areas with residual amplitudes of 1 - 2 cm (Fig. 2).

 

Fig. 1 Residual amplitudes of tidal constiuents in the Yellow Sea - relative to FES2004, which was used as reference model. For M2 and S2 the resdiuals exceed 15 cm. K2, O1, and K1 show residual amplitudes of about 5 cm. Fig 2. Global distribution of residual amplitudes for M2 (top panel) and S2 (bottom panel). Even in open ocean there are extended areas with residual amplitudes of 1 - 2; 2 cm for both M2 and S2.

The EOT08a model can be downloaded at the anonymous ftp://ftp.dgfi.badw.de/ . In the directory pub/EOT08a/dat grid files for all constituents are given in both, netcdf format and an ASCII format, compatible with the FES2004 grids.

 

The impact on GRACE processing is subject to further research activity in the DAROTA project of the DFG priority program SPP1257 (Bosch et al., 2009). Evaluating GRACE data and models with EOT08a show a gain in GRACE K-band data.

 

  • Savcenko R., Bosch W.: EOT08a − empirical ocean tide model from multi-mission satellite altimetry. DGFI Report No. 81, Deutsches Geodätisches Forschungsinstitut (DGFI), München, 2008
  • Bosch W., R. Savcenko, F. Flechtner, Ch. Dahle, T. Mayer-Gürr, D. Stammer, E. Taguchi, and K.-H. Ilk (2009) Residual ocean tide signals from satellite altimetry, GRACE gravity fields, and hydrodynamic modelling. Submitted as GJI-09-0056 to Geophysical Journal International.