30
V. Cardin and L. Ursella
may indicate the presence of an anticyclonic circulation opposite to that observed in the surface
layer.
The vertical sections of the studied parameters across the Adriatic Sea during this period
show the deepening of the thermocline from the
north to south. At the northern end of the basin,
the thermocline is positioned at about 8-10 m
depth, while in the southern part (transect E), it
almost reaches the bottom (5 m from the bottom). In Fig. 4, three vertical sections are presented corresponding to transect C, located off
the northern mouth of the Po river, transect D
off the southern mouth and transect E situated
in the southern part of the studied area.
Generally, the salinity conditions the sigma-t
distribution above the thermocline, while below
it, the temperature is the more important controlling factor. The doming of the isopycnals in
the intermediate layer tends to divide the surface layer into two parts indicating the presence
of various mesoscale cyclonic and anticyclonic
structures.
For what concerns the analysis of the ADCP
data, the overall length of the data record permits to calculate only the M2 tidal component.
The transport ellipses obtained for M2 are
polarised in the centre of the basin along the
NW -SE direction (coincident with the Adriatic
45.5
45
~ 44.5
.2
~
44
43.5
, "' .......
~
"''''''x..''x..
, ''''''x..''x...''x... }
"
... "x..."x..."x...
, , ........... "x... • .,..:)(,.
, .........................
..... ,"" ..........
........................
~:::::::::
"" ............
......... .....
10 m 2 /s
12.5 13 13.5 14
longitude
Fig. 5. Tidal transport ellipses for the M2 tidal component
longitudinal axis), while near the Italian coast
they change their orientation, almost following
the shoreline. The maximum tidal amplitude is
found in the central part of the Adriatic Sea
where the major semi-axals shows values of
around 6 m 2 /s corresponding to a velocity of 10
cm/s; the minimum is found immediately north
of the Po river delta, where the major semi-axis
decreases to 0.5 m 2 /s with a corresponding velocity of about 1 cmls (Fig. 5). In the central part of
the basin the behaviour of the tidal transport
ellipses is coherent with the results obtained
from numerical models (Cavallini 1985; Maladc
et al. 1998). On the contrary, in the northernmost
part, just outside the Gulf of Trieste, the ellipses
in general have smaller semi-axes and they are
rotated by about 90 degrees with respect to the
ones coming from the models; this is probably
due to insufficient data coverage in these zones
and to the lack. of imposition of boundary conditions.
The structure obtained for the steady part of
the current field shows a southward current
along the Italian coast, as well as the tendency to
maintain a sub-basin cyclonic circulation in the
northernmost area to the north of the Po River
delta (Fig. 6). The existence of this cyclone has
already been revealed by Borzelli et al. (1992)
with a surface drifter experiment. The structure
45.5
45
.g 44.5
.2
N
44
43.5
", -"I i o. . . o:-_\,,"
,-.,. ..... -
. .. " ........
......... ....
0.1 mls
12 m depth
12.5 13 13.5 14
longitude
Fig. 6. Horizontal distribution of steady currents at 12 m
depth. Data locations are indicated
V. Cardin and L. Ursella
may indicate the presence of an anticyclonic circulation opposite to that observed in the surface
layer.
The vertical sections of the studied parameters across the Adriatic Sea during this period
show the deepening of the thermocline from the
north to south. At the northern end of the basin,
the thermocline is positioned at about 8-10 m
depth, while in the southern part (transect E), it
almost reaches the bottom (5 m from the bottom). In Fig. 4, three vertical sections are presented corresponding to transect C, located off
the northern mouth of the Po river, transect D
off the southern mouth and transect E situated
in the southern part of the studied area.
Generally, the salinity conditions the sigma-t
distribution above the thermocline, while below
it, the temperature is the more important controlling factor. The doming of the isopycnals in
the intermediate layer tends to divide the surface layer into two parts indicating the presence
of various mesoscale cyclonic and anticyclonic
structures.
For what concerns the analysis of the ADCP
data, the overall length of the data record permits to calculate only the M2 tidal component.
The transport ellipses obtained for M2 are
polarised in the centre of the basin along the
NW -SE direction (coincident with the Adriatic
45.5
45
~ 44.5
.2
~
44
43.5
, "' .......
~
"''''''x..''x..
, ''''''x..''x...''x... }
"
... "x..."x..."x...
, , ........... "x... • .,..:)(,.
, .........................
..... ,"" ..........
........................
~:::::::::
"" ............
......... .....
10 m 2 /s
12.5 13 13.5 14
longitude
Fig. 5. Tidal transport ellipses for the M2 tidal component
longitudinal axis), while near the Italian coast
they change their orientation, almost following
the shoreline. The maximum tidal amplitude is
found in the central part of the Adriatic Sea
where the major semi-axals shows values of
around 6 m 2 /s corresponding to a velocity of 10
cm/s; the minimum is found immediately north
of the Po river delta, where the major semi-axis
decreases to 0.5 m 2 /s with a corresponding velocity of about 1 cmls (Fig. 5). In the central part of
the basin the behaviour of the tidal transport
ellipses is coherent with the results obtained
from numerical models (Cavallini 1985; Maladc
et al. 1998). On the contrary, in the northernmost
part, just outside the Gulf of Trieste, the ellipses
in general have smaller semi-axes and they are
rotated by about 90 degrees with respect to the
ones coming from the models; this is probably
due to insufficient data coverage in these zones
and to the lack. of imposition of boundary conditions.
The structure obtained for the steady part of
the current field shows a southward current
along the Italian coast, as well as the tendency to
maintain a sub-basin cyclonic circulation in the
northernmost area to the north of the Po River
delta (Fig. 6). The existence of this cyclone has
already been revealed by Borzelli et al. (1992)
with a surface drifter experiment. The structure
45.5
45
.g 44.5
.2
N
44
43.5
", -"I i o. . . o:-_\,,"
,-.,. ..... -
. .. " ........
......... ....
0.1 mls
12 m depth
12.5 13 13.5 14
longitude
Fig. 6. Horizontal distribution of steady currents at 12 m
depth. Data locations are indicated