Assimilating data into a tidal model of the Irish and Celtic Seas

A data assimilation procedure, which has successfully been applied to global ocean tide models, is briefly described and applied to the shelf sea area of the Irish and Celtic Seas. The frequency-dependent model of theM2 tide used in the assimilation procedure incorporates the full load and self-attraction effect by evaluating the convolution integral using Greenʹs function for potential perturbation, bottom deformation and self-attraction. A grid resolution of 5′ north-south and west-east is accompanied by both a realistic reproduction of theM2 tide in the Irish and Celtic Seas and an accurate determination of the short-distance effect of loading and self-attraction. Whilst assimilating 14 offshore tidal elevation data, the mass is exactly conserved. The statistic properties of the model, e.g. the connection between the weights matrix and the error covariance matrix, are briefly derived. Along the open boundaries of the model area, sea surface topography values from a global12° model are specified.A posteriori the variance of these boundary values is statistically estimated from the residuals. This estimate is used in a successive correction mechanism to get a new set of boundary values. The direct solution as well as the solution influenced by the data agrees much better with the elevation and current data using the set of boundary values obtained in this way.