The 2023 astronomical tide predictions for the Gulf of Trieste, with updated harmonic constants, were realized by the Alpine-Adriatic Meteorological Society as part of the technical-scientific framework Agreement in the fields of climatology, meteorology and oceanography between A-AMS (UMFVG onlus) and the Institute of Marine Sciences of the National Research Council (ISMAR).
This issue here available has been edited by Fabio Raicich (Data processing and astronomical tide prediction), Andrea Securo (layout and text revision) and Renato R. Colucci (realization of tidal curves and tables).
The sea-level variability
The sea level variability depends on several factors, the most important being the astronomical tide, the meteorological forcing, the thermohaline properties (temperature and salinity) of the water mass, and the global climatic variations.
If the mean sea level, typically computed over 3 or 6 months, and the astronomical tide are subtracted from the observed sea level, one obtains the “residual sea level” or “meteorological tide”, which essentially accounts for the effect of the meteorological forcing.
Effects of the astronomical tide
The astronomical tide is the product of the gravitational attraction exerted by the Moon and the Sun on the oceanic mass, and it depends on the position of the
Earth relative to the two celestial bodies. Because the relative motion of such bodies is known with high precision, the tide evolution caused by their interactions is also predictable with high accuracy, unlike, for instance, the meteorological forecast.
On the north Adriatic coast, the tide prevailingly exhibits two highs and two lows per day (semidiurnal type). At the new Moon and full Moon (sizigie) this phenomenon is more marked and the largest tidal ranges occur. At the first and last quarters (quadrature) the tidal range is less marked, often with only one high and one low per day (diurnal type).