# Observing Meteorological Tides: Fifteen Years of Statistics in the Port of La Spezia (Italy)
###### Abstract  
Sea level changes in coastal areas significantly influence port activities (e.g., the safety of navigation). Along Italian coastlines, sea level variations are mainly due to astronomical tides (well known, due to gravitational attraction between Earth, Moon and Sun); however, during the last fifteen years, a high number of \"anomalous\" tides has been observed: the study of the phenomenon has allowed to attribute its cause to variations in atmospheric pressure (the so-called meteorological tides: sea level drops when atmospheric pressure increases and vice versa); the statistical analysis of acquired data made it possible to evaluate the hydrobarometric transfer factor (a local parameter which represents the correlation between atmospheric pressure changes and consequent sea level variations): it was found that it is usually much larger within gulfs or port basins than offshore areas, where a pressure change of 1 hPa results in a sea level variation of about 1 cm; the statistical analysis described in the following, and aimed at correctly estimating the hydrobarometric transfer factor in harbors, can play a fundamental role in optimizing the management of port waters: its results allow to forecast meteorological tides and therefore future sea level (and depth) variations in a given port basin. The results of the study conducted in the port of La Spezia (North Western Italy) are presented here, together with possible applications on port activities and harbor water management. meteorological tides; marine environmental monitoring; sea level forecasting; harbor water management; port navigation safety +
Footnote †: journal: Applied Sciences  
The evidence of the phenomenon was observed by means of ISPRA's (Italian Institute for Environmental Protection and Research) meteo-mareographic station located in La Spezia harbor (Italy); for example, on 13 November 2020 at 10:15 UTC (Universal Time Coordinates) and on 8 December 2020 at 09:25 UTC, the same astronomical tide was present (nearly 20 cm), but a pressure decrease of nearly 27.1 hPa resulted in an increase of about 34 cm in the sea level acquired. In many Italian ports, we have verified that the hydrobarometric transfer factor, a parameter that represents the correlation between the atmospheric pressure variation and the consequent change in sea level, assumes often much larger values (even double) compared with offshore areas, where, as is well known, 1 hPa (about equal to 1 mBar) of atmospheric pressure variation corresponds to approximately 1 cm of change in sea level (the so-called inverted barometer effect); so, within harbors, a few hPa of decrease/increase in atmospheric pressure can cause several cm of sea level rise/fall; in fact, a sea basin behaves in the same way as a semi-constrained domain: by hindering the horizontal movement of the water mass, it amplifies its vertical displacement. Therefore, meteorological tides can cause exceptional changes in sea level within a port basin if they occur in-phase with astronomical ones. To be able to forecast sea level in harbors, it is therefore necessary to estimate the correlation between atmospheric pressure and sea level, represented by the hydrobarometric transfer factor; it depends on a series of local parameters (first of all the morphology of the basin examined and the atmospheric dynamics over it), so it is not described by a deterministic law valid everywhere but obtained port by port through a statistical analysis of local data acquired [24; 25; 26; 27; 28; 29; 30; 31].