New insights on the Venice high-water phenomenon through a maximum negentropy criterium

Abstract

A multiparametric analysis of the sea level oscillations in the Venetian lagoon (Italy) is performed in order to study a period in which the Venice lagoon system experiences excited states without becoming predominant in the dynamics of the system. We report the results relative to 2008, for which the Relative Sea Level time evolution is well balanced between stationary states and excited states (when high-water episodes can occur). The interest is devoted to the high-water phenomenon in order to give indications on the generating dynamical system. Looking at time scales of the order of 7 days, the application of the spectral analysis and a high-order decomposition method allows the identification and extraction of diurnal, semidiurnal, ter-diurnal, and sometimes quarter-diurnal tides. The ratio among the constituents’ amplitudes as a function of the meteorological forcing, together with the extraction of the quarter-diurnal, evidence some nonlinearity in high-water occurrence. A conceptual model is proposed that takes into account the nonlinearity evidenced in the system. The extracted tidal constituents are seen as globally organized oscillations generated by a self-oscillating system showing a behaviour like the flue musical instruments, with a non-trivial relation between amplitude and frequency. The stationary state (no high-water) and the anomalous tides can be seen as different states of such a nonlinear system.