23 research outputs found
Circulation in the Gulf of Trieste: Measurements and model results
The study presents seasonal variability of currents in the Southern part of the Gulf of Trieste. A time series analysis of currents and wind stress for the period
2003-2006, which were measured by the coastal oceanographic buoy, was conducted. A comparison between these data and results obtained from a numerical model of circulation in the Gulf was performed to validate model results. Three
different approaches were applied to the wind data to determine the wind stress. Similarities were found between Kondo and Smith approaches while the method of Vera shows differences which were particularly noticeable for lower
(= 1m/s) and higher wind speeds (= 15 m/s). Mean currents in the surface layer are generally outflow currents from the Gulf due to wind forcing (bora). However in all other
depth layers inflow currents are dominant. With the principal component analysis (PCA) major and minor axes were determined for all seasons. The major axis of maximum variance in years between 2003 and 2006 is prevailing in
NE-SW direction, which is parallel to the coastline. Comparison of observation and model results is showing that currents are similar (in direction) for the surface and bottom layers but are significantly different for the middle layer (5–13m). At a depth between 14–21m velocities are comparable in direction as well as in magnitude even though model values are higher. Higher values of modelled currents at the surface and near the bottom are explained by higher values of wind stress that were used in the model
as driving input with respect to the stress calculated from the measured winds. Larger values of modelled currents near the bottom are related to the larger inflow that needs to compensate for the larger modelled outflow at the surface. However, inspection of the vertical structure of temperature, salinity and density shows that the model is reproducing a weaker density gradient which enables the penetration of the outflow surface currents to larger depths
Influence of topography on tide propagation and amplification in semi-enclosed basins
An idealized model for tide propagation and amplification in semi-enclosed rectangular basins is presented, accounting for depth differences by a combination of longitudinal and lateral topographic steps. The basin geometry is formed by several adjacent compartments of identical width, each having either a uniform depth or two depths separated by a transverse topographic step. The problem is forced by an incoming Kelvin wave at the open end, while allowing waves to radiate outward. The solution in each compartment is written as the superposition of (semi)-analytical wave solutions in an infinite channel, individually satisfying the depth-averaged linear shallow water equations on the f plane, including bottom friction. A collocation technique is employed to satisfy continuity of elevation and flux across the longitudinal topographic steps between the compartments. The model results show that the tidal wave in shallow parts displays slower propagation, enhanced dissipation and amplified amplitudes. This reveals a resonance mechanism, occurring when\ud
the length of the shallow end is roughly an odd multiple of the quarter Kelvin wavelength. Alternatively, for sufficiently wide basins, also Poincaré waves may become resonant. A transverse step implies different wavelengths of the incoming and reflected Kelvin wave, leading to increased amplitudes in shallow regions and a shift of amphidromic points in the direction of the deeper part. Including the shallow parts near the basin’s closed end (thus capturing the Kelvin resonance mechanism) is essential to reproduce semi-diurnal and diurnal\ud
tide observations in the Gulf of California, the Adriatic Sea and the Persian Gulf
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Turbulence observations in the Gulf of Trieste under moderate wind forcing and different water column stratification
The oceanographic campaign CARPET2014 (Characterizing Adriatic Region Preconditionig EvenTs), (30 January–4 February 2014) collected the very first turbulence data in the
Gulf of Trieste (northern Adriatic Sea) under moderate wind (average wind
speed 10 m s<sup>−1</sup>) and heat flux (net negative heat flux ranging from 150
to 400 W m<sup>−2</sup>). Observations consisted of 38 CTD (Conductivity, Temperature, Depth) casts and 478
microstructure profiles (grouped into 145 ensembles) with three sets of yoyo
casts, each lasting for about 12 consecutive hours. Averaging closely
repeated casts, such as the ensembles, can lead to a smearing effect when in
the presence of a vertical density structure with strong interfaces that can
move up or down between subsequent casts under the influence of tides and
internal waves. In order to minimize the smearing effect of such
displacements on mean quantities, we developed an algorithm to realign
successive microstructure profiles to produce sharper and more meaningful
mean profiles of measured turbulence parameters.
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During the campaign, the water column in the gulf evolved from well-mixed to
stratified conditions due to Adriatic waters intruding at the bottom along
the gulf's south-eastern coast. We show that during the warm and relatively
dry winter, the water column in the Gulf of Trieste, even under moderate wind
forcing, was not completely mixed due to the influence of bottom waters
intruding from the open sea. Inside the gulf, two types of water intrusions
were found during yoyo casts: one coming from the northern
coast of the Adriatic Sea (i.e. cooler, fresher and more turbid) and one coming from the open
sea in front of the Po Delta (i.e. warmer, saltier and less turbid). The two
intrusions had different impacts on turbulence kinetic energy dissipation
rate profiles. The former, with high turbidity, acted as a barrier to
wind-driven turbulence, while the latter, with low sediment concentrations
and a smaller vertical density gradient, was not able to suppress downward
penetration of turbulence from the surface