Abstract
Test runs for the Region of Freshwater Influence (ROFI) in the Gulf of
Trieste were setup using the ‘Nucleus for European Modelling of the
Ocean’ (NEMO) model. Two test simulations of plume spreading were
performed: the first was run for the winter season with initially
homogeneous water and a constant bora wind blowing along the Gulf’s axis
with a speed of 13 The second simulation was run for summer conditions
with vertically stratified water and without wind forcing. The -
turbulence scheme on an Arakawa C-type grid common for NEMO, was applied
as described in (Madec, 2008). The modeled area of the Gulf, 31.8 33 km,
is gridded in cells of dimension 0.6 km 0.6 km, similar to the model
setup in (Žagar et al. 2013). A simplification of the OBC was achieved
by extending the domain by 15 km in a westward direction, and by closing
the simulation area. Along the vertical, 25 z-layers were inserted. The
forcing of the river Soča (Isonzo) was simulated with the conversion of
the volume flow-rates for the summer (120 ) and winter (150 ) situations
to the vertical mass density flow through the topmost cell by applying
discharges of 0.33 and 0.42 , respectively. The river temperature was
set to the ambient temperature, while the salinity of the river runoff
was set to 0 PSU. Both simulations run for the period of 48h, when the
nearly ‘steady’ state was reached. The winter simulation revealed a
strong outflow current in the form of a belt of fresher water, attached
to the northern coastline of the Gulf. This is mainly a wind-driven
process, and in this case the salinity acts as a passive tracer. The
water mass returns through the deeper layers in the central and southern
parts of the Gulf, according to the topographic control (Malačič et al.
2012). In the summer windless simulation, radial spreading of the
freshwater stemming from the Soča River is present in the inertial plume
area. The velocity vectors deflect due to the Coriolis force, forming
outward spiraling paths of surface parcels. Once the scaling of terms in
the equation of motion is completed, the transient situations with
variable winds, tides, and the river flow rate can be tackled, as
(Querin et al. 2007). Madec, G., 2008. Nemo Ocean Engine. Note du Pôle
de modélisation, Institut Pierre-Simon Laplace (IPSL), France, pp. 396.
Malačič, V., B. Petelin, and M. Vodopivec, 2012: Topographic Control of
Wind-driven Circulation in the Northern Adriatic. Journal of Geophysical
Research: Oceans, 117, 1–16. Querin, S., A. Crise, D. Deponte, and C.
Solidoro, 2007: 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). Journal of Geophysical
Research, 111, 1–19. Žagar, D., E. Džebo, and G. Petkovšek, 2013:
Comparison of Models MIKE3 and PCFLOW3D: Hydrodynamic Simulations in the
Gulf of Trieste –Acta hydrotechnica, 26, 117–133.