engleski

Estimating the Adriatic Sea tidal open boundary conditions: From a reduced model dynamics to data assimilation

This study addresses the question of properly forcing the co-oscillating Adriatic tides. The Adriatic Sea is an elongated land-locked Mediterranean sub-basin with a fairly complex tidal structure, although not of exceptional harmonic amplitudes. The specification of the open boundary conditions is one of the promising application areas for the data assimilation methods. In order to examine the Adriatic response to major tidal harmonics (M2, S2, KI, 01) we have relied on a series of numerical models. We started with a non-linear dynamical model forced at the Straits of Otranto by the results of a Mediterranean tidal modeling study (Tsimplis et al., 1995). A 2D linear barotropic model was then used to assimilate the Adriatic tide gauge data and obtain optimal boundary conditions. Typically, such a model can fit the sea level data rather well, but does not provide information about the 3D current structure. Hence, we have then used a 3D finite element model (Quoddy - Lynch et al., 1996) forced at the Otranto by a literature-derived set of empirical boundary conditions (Poli, 1960). Although in line with known Adriatic tidal behaviour these results warrant further considerations of the boundary conditions. Consequently, in the final step we have used a combination of a forward 3D model (Quoddy) and 2D linear assimilative model, following the so called incremental approach (Thompson et al., 1998). The goal has been to obtain the optimal boundary conditions for the 3D model, by assimilating the tide gauge data via a simpler 2D code. First, the observations are assimilated into the 2D model, which then provides the open boundary conditions to force the Quoddy. The residuals from the 3D model are then assimilated back into the 2D model to provide a new set of the open boundary conditions for Quoddy. The procedure is iterated until the convergence criterion is met. The results obtained so far suggest encouraging improvements over the regular 3D runs, providing dynamically consistent estimate of the open boundary conditions. We expect that the open boundary conditions thus obtained will enable us to successfully investigate more demanding aspects of the Adriatic tidal dynamics.

Adriatic Sea; tidal modeling; data assimilation

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