Hydrology of the Northern Adriatic
31
Fig. 7. Po river discharge for
October-November 1997
3500 . - - - - - - - - - - - - - - - - - - - - - - - - - - - - ,
3000
~
.. 2000
0:
.=
u
'"
is 1500
~
~
Q
ilion
Q.o
suu
Prisma2 Autumn Campaign
.
,
u ~-------~----------~---------------~
cptcmbc,·
found in the steady field is maintained almost
throughout the water column and its behaviour
seems to be barotropic, at least concerning the
main features. It should be remembered that
these velocities are representative of the general
behaviour of the circulation over the whole campaign considered; therefore the barotropic
behaviour is probably due to the fact that, for the
most part of the period. the water column is
homogenised over the major part of the studied
area. Finally it must be pointed out that the
steady field accounts for the basin-wide general
circulation, but not for the small scale structures.
On the contrary, the residual pattern changes
from transect to transect, reflecting the variability associated with river discharges and
mesoscale structures. Therefore, it presents a
more complicated structure and shows occasionally the presence of a northward flowing current
along the Italian coast. This feature is unusual if
seen in terms of the Adriatic general circulation,
but it must be remembered that the residual field
presents a variability on the order of several
days, and to obtain the measured current at one
point, the steady and tidal terms must be added
to this one. From the Po river discharge (Fig. 7),
it is evident that no important pulses are present
during the studied period, so that no strong
southward residual flow is expected at any of the
transects situated in front or to the south of the
Po river delta. This means that no direct response
is expected and any eventual current has to be
explained in terms of wind effects or mesoscale
October
Nm·ember
structures detached from the coastal steady current. The vertical distribution of the residual current components perpendicular to transects C
(data collected on 27/09/97), D (data collected on
27/09/98) and E (data collected on 28/09/97), is
depicted in Figs. 8,9 and 10, respectively. It shows
dearly that effectively no southward flow is present at transects D and E. The only exception is
transect C, for which the velocity pattern can be
explained in terms of a mesoscale eddy detached
from the mean southward current. A strong
southward flow is also present at some transects
in the northernmost part of the studied area. All
of this zone is characterised by an along-shore
narrow current due to the discharge of rivers,
that flows along the Italian coast with the coast
on the right. Unfortunately, no data about the
discharge of these rivers are available. Looking at
these sections in detail, it can be seen that transect A presents a southward velocity in correspondence to the Tagliamento river mouth, while
the rest of the section is occupied by the northward current. Perhaps this is due to the fact that
the transect is distant from the coast and it does
not reach the coastal boundary layer; also, the
ADCP data do not cover completely the hydrological section. Proceeding with the sections
toward the south, the southern flow on the western side becomes stronger, reaching the maximum just south of the southernmost mouth of
the Venice lagoon. As the dimensions of the current reversals are of the order of 10 km, the
observed structures could be associated with
31
Fig. 7. Po river discharge for
October-November 1997
3500 . - - - - - - - - - - - - - - - - - - - - - - - - - - - - ,
3000
~
.. 2000
0:
.=
u
'"
is 1500
~
~
Q
ilion
Q.o
suu
Prisma2 Autumn Campaign
.
,
u ~-------~----------~---------------~
cptcmbc,·
found in the steady field is maintained almost
throughout the water column and its behaviour
seems to be barotropic, at least concerning the
main features. It should be remembered that
these velocities are representative of the general
behaviour of the circulation over the whole campaign considered; therefore the barotropic
behaviour is probably due to the fact that, for the
most part of the period. the water column is
homogenised over the major part of the studied
area. Finally it must be pointed out that the
steady field accounts for the basin-wide general
circulation, but not for the small scale structures.
On the contrary, the residual pattern changes
from transect to transect, reflecting the variability associated with river discharges and
mesoscale structures. Therefore, it presents a
more complicated structure and shows occasionally the presence of a northward flowing current
along the Italian coast. This feature is unusual if
seen in terms of the Adriatic general circulation,
but it must be remembered that the residual field
presents a variability on the order of several
days, and to obtain the measured current at one
point, the steady and tidal terms must be added
to this one. From the Po river discharge (Fig. 7),
it is evident that no important pulses are present
during the studied period, so that no strong
southward residual flow is expected at any of the
transects situated in front or to the south of the
Po river delta. This means that no direct response
is expected and any eventual current has to be
explained in terms of wind effects or mesoscale
October
Nm·ember
structures detached from the coastal steady current. The vertical distribution of the residual current components perpendicular to transects C
(data collected on 27/09/97), D (data collected on
27/09/98) and E (data collected on 28/09/97), is
depicted in Figs. 8,9 and 10, respectively. It shows
dearly that effectively no southward flow is present at transects D and E. The only exception is
transect C, for which the velocity pattern can be
explained in terms of a mesoscale eddy detached
from the mean southward current. A strong
southward flow is also present at some transects
in the northernmost part of the studied area. All
of this zone is characterised by an along-shore
narrow current due to the discharge of rivers,
that flows along the Italian coast with the coast
on the right. Unfortunately, no data about the
discharge of these rivers are available. Looking at
these sections in detail, it can be seen that transect A presents a southward velocity in correspondence to the Tagliamento river mouth, while
the rest of the section is occupied by the northward current. Perhaps this is due to the fact that
the transect is distant from the coast and it does
not reach the coastal boundary layer; also, the
ADCP data do not cover completely the hydrological section. Proceeding with the sections
toward the south, the southern flow on the western side becomes stronger, reaching the maximum just south of the southernmost mouth of
the Venice lagoon. As the dimensions of the current reversals are of the order of 10 km, the
observed structures could be associated with