Assimilation of Co-Amplitudes in the Barotropic Tidal Modul

Our work is focused on tidal simulations in the OMCT. In the so-called barotropic version, all driving forces are deactivated apart from the tidal force. The ocean is treated as homogenous (i.e. with no density differences).
The luni-solar tidal potential is decomposed into partial tides via Fourier transformation. To get an estimate of the accuracy of the calculated sea-surface heights (co-amplitudes) created by the partial tides, we compare them with the pelagic database st103. This database consists of data (co-amplitudes) collected at 103 tide gauge measuring stations in the open ocean.
Comparing the model results with the data, it can be clearly seen that the model slightly underestimates the co-amplitudes (see figure above). We therefore use the variational assimilation to improve the model. This assimilation method tries to decrease the model-data deviation under the constraint that the governing physical equations remain valid, by changing model parameters via the assimilation routine.
Since sea-surface heights are strongly influenced by the shape of the underlying oceanic bottom (interferences), which is still not known with high accuracy, we define an additional term added to the tidal potential, to correct interferences created by the insufficiently known bathymetry. With this ansatz, the model-data deviations could be reduced by up to 15% (see lower figure).

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Jan Saynisch-Wagner
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Dr. Jan Saynisch-Wagner
Earth System Modelling
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