Modelling the sea level in the Mediterranean Sea by assimilating data from coastal stations

In this work, we have used a hydrodynamic finite element model to study tides, surges and seiches in the Mediterranean Sea. The simulations were performed with and without data assimilation for a two-month period, November and December 2019, in which several intense meteorological events occurred in this area. The observations come from coastal stations along the Mediterranean and have been processed to select tides and surges. Surge simulations were used also to analyse seiche oscillations in the Mediterranean. These oscillations are caused by an initial perturbation and propagate freely with periods corresponding to the barotropic modes of the basin. The periods and the energy have been identified through spectral analysis from the observed data and their forecast improves significantly with data assimilation. Furthermore, data assimilation in reanalysis simulations shows a significantly improving in the results, both for the surge and for the astronomical tide. The error of the results reduces considerably even in areas far from the assimilated stations, such as the Eastern Mediterranean Sea. In the case of the astronomical tide, a comparison with the tide calculated from the harmonic components, extrapolated by altimetric data, demonstrates a considerable improvement not only in the coastal areas but also in the central part of the basin. This study is the first step to set up long-term reanalysis climatological simulations for tides, surges and total sea level in the Mediterranean Sea.