Numerical study of the role of wind forcing and freshwater buoyancy input on the circulation in a shallow embayment (Gulf of Trieste, Northern Adriatic Sea)

[ 1] This paper investigates the role of wind forcing and river discharge on a small-scale shallow embayment: the Gulf of Trieste. The qualitative and quantitative analysis of these dominant processes is carried out using a high resolution numerical model, initialized and forced with experimental data. The simulations are focused on short-term transient events, which occurred during the stratification season ( spring and summer). Two significant case studies are analyzed in detail: a strong wind event during summer and a river flood during spring. The model output is also checked against the results of a nondimensional scale analysis and against buoy and satellite observed data. These comparisons show a good correlation, validating the numerical simulations for the two case studies. The model shows that strong wind events blowing on stably stratified water cause coastal upwelling and almost entirely mix the water column in a few hours. Strong wind-driven currents can flush the whole basin in almost 3 days. On the contrary, river floods affect mainly the upper layer, down to 5 m. The circulation is estuarine with a sharp vertical density gradient and horizontal fronts at the interface between plume freshwater and ambient salty water. Given the length scale of the basin, the effect of rotation is weak and a local coastal current in geostrophic balance is not formed during the simulated time period ( 20 days).